Added error checking (EFAULT) for null arguments

* Fixed zmq_term, zmq_socket, zmq_close, zmq_setsockopt,
* zmq_getsockopt, zmq_bind, zmq_connect, zmq_send,
* zmq_recv, zmq_poll, zmq_device, zmq_stopwatch_stop
* Updated Reference Manual for these methods

doc/zmq_bind.txt

@@ -61,6 +61,8 @@ The requested 'address' was not local.
 The requested 'address' specifies a nonexistent interface.
 *ETERM*::
 The 0MQ 'context' associated with the specified 'socket' was terminated.
+*EFAULT*::
+The provided 'socket' was not valid (NULL).
 
 
 EXAMPLE

doc/zmq_close.txt

@@ -31,7 +31,8 @@ return `-1` and set 'errno' to one of the values defined below.
 
 ERRORS
 ------
-No errors are defined.
+*EFAULT*::
+The provided 'socket' was not valid (NULL).
 
 
 SEE ALSO

doc/zmq_connect.txt

@@ -59,6 +59,8 @@ The requested 'transport' protocol is not supported.
 The requested 'transport' protocol is not compatible with the socket type.
 *ETERM*::
 The 0MQ 'context' associated with the specified 'socket' was terminated.
+*EFAULT*::
+The provided 'socket' was not valid (NULL).
 
 
 EXAMPLE

doc/zmq_device.txt

@@ -89,8 +89,17 @@ Refer to linkzmq:zmq_socket[3] for a description of these socket types.
 
 RETURN VALUE
 ------------
-The _zmq_device()_ function always returns `-1` and 'errno' set to *ETERM* (the
-0MQ 'context' associated with either of the specified sockets was terminated).
+The _zmq_device()_ function shall not return if successful. Otherwise it shall
+return `-1` and set 'errno' to one of the values defined below.
+
+
+ERRORS
+------
+*ETERM*::
+The 0MQ 'context' associated with the specified 'frontend' or 'backend' was 
+terminated.
+*EFAULT*::
+The provided 'frontend' or 'backend' was not valid (NULL).
 
 
 EXAMPLE

doc/zmq_getsockopt.txt

@@ -214,6 +214,8 @@ _option_value_, as specified by _option_len_, is insufficient for storing the
 option value.
 *ETERM*::
 The 0MQ 'context' associated with the specified 'socket' was terminated.
+*EFAULT*::
+The provided 'socket' was not valid (NULL).
 
 
 EXAMPLE

doc/zmq_poll.txt

@@ -96,6 +96,8 @@ to a different application thread.
 *ETERM*::
 At least one of the members of the 'items' array refers to a 'socket' whose
 associated 0MQ 'context' was terminated.
+*EFAULT*::
+The provided 'items' was not valid (NULL).
 
 
 EXAMPLE

doc/zmq_recv.txt

@@ -63,6 +63,8 @@ socket types that switch between several states, such as ZMQ_REP.  See the
 _messaging patterns_ section of linkzmq:zmq_socket[3] for more information.
 *ETERM*::
 The 0MQ 'context' associated with the specified 'socket' was terminated.
+*EFAULT*::
+The provided 'socket' was not valid (NULL).
 
 
 EXAMPLE

doc/zmq_send.txt

@@ -69,6 +69,8 @@ socket types that switch between several states, such as ZMQ_REP.  See the
 _messaging patterns_ section of linkzmq:zmq_socket[3] for more information.
 *ETERM*::
 The 0MQ 'context' associated with the specified 'socket' was terminated.
+*EFAULT*::
+The provided 'context' was not valid (NULL).
 
 
 EXAMPLE

doc/zmq_setsockopt.txt

@@ -229,6 +229,8 @@ The requested option _option_name_ is unknown, or the requested _option_len_ or
 _option_value_ is invalid.
 *ETERM*::
 The 0MQ 'context' associated with the specified 'socket' was terminated.
+*EFAULT*::
+The provided 'socket' was not valid (NULL).
 
 
 EXAMPLE

doc/zmq_socket.txt

@@ -242,9 +242,10 @@ ERRORS
 ------
 *EINVAL*::
 The requested socket 'type' is invalid.
-
 *EMTHREAD*::
 The maximum number of sockets within this 'context' has been exceeded.
+*EFAULT*::
+The provided 'context' was not valid (NULL).
 
 
 SEE ALSO

doc/zmq_term.txt

@@ -43,7 +43,8 @@ return `-1` and set 'errno' to one of the values defined below.
 
 ERRORS
 ------
-No errors are defined.
+*EFAULT*::
+The provided 'context' was not valid (NULL).
 
 
 SEE ALSO

src/zmq.cpp

@@ -275,7 +275,10 @@ int zmq_term (void *ctx_)
     int rc = ((zmq::ctx_t*) ctx_)->term ();
     int en = errno;
 
-    zmq_assert (ctx_);
+    if (!ctx_) {
+        errno = EFAULT;
+        return -1;
+    }
 #if defined ZMQ_HAVE_OPENPGM
     //  Shut down the OpenPGM library.
     if (pgm_shutdown () != TRUE)
@@ -288,13 +291,19 @@ int zmq_term (void *ctx_)
 
 void *zmq_socket (void *ctx_, int type_)
 {
-    zmq_assert (ctx_);
+    if (!ctx_) {
+        errno = EFAULT;
+        return NULL;
+    }
     return (void*) (((zmq::ctx_t*) ctx_)->create_socket (type_));
 }
 
 int zmq_close (void *s_)
 {
-    zmq_assert (s_);
+    if (!s_) {
+        errno = EFAULT;
+        return -1;
+    }
     ((zmq::socket_base_t*) s_)->close ();
     return 0;
 }
@@ -302,39 +311,57 @@ int zmq_close (void *s_)
 int zmq_setsockopt (void *s_, int option_, const void *optval_,
     size_t optvallen_)
 {
-    zmq_assert (s_);
+    if (!s_) {
+        errno = EFAULT;
+        return -1;
+    }
     return (((zmq::socket_base_t*) s_)->setsockopt (option_, optval_,
         optvallen_));
 }
 
 int zmq_getsockopt (void *s_, int option_, void *optval_, size_t *optvallen_)
 {
-    zmq_assert (s_);
+    if (!s_) {
+        errno = EFAULT;
+        return -1;
+    }
     return (((zmq::socket_base_t*) s_)->getsockopt (option_, optval_,
         optvallen_));
 }
 
 int zmq_bind (void *s_, const char *addr_)
 {
-    zmq_assert (s_);
+    if (!s_) {
+        errno = EFAULT;
+        return -1;
+    }
     return (((zmq::socket_base_t*) s_)->bind (addr_));
 }
 
 int zmq_connect (void *s_, const char *addr_)
 {
-    zmq_assert (s_);
+    if (!s_) {
+        errno = EFAULT;
+        return -1;
+    }
     return (((zmq::socket_base_t*) s_)->connect (addr_));
 }
 
 int zmq_send (void *s_, zmq_msg_t *msg_, int flags_)
 {
-    zmq_assert (s_);
+    if (!s_) {
+        errno = EFAULT;
+        return -1;
+    }
     return (((zmq::socket_base_t*) s_)->send (msg_, flags_));
 }
 
 int zmq_recv (void *s_, zmq_msg_t *msg_, int flags_)
 {
-    zmq_assert (s_);
+    if (!s_) {
+        errno = EFAULT;
+        return -1;
+    }
     return (((zmq::socket_base_t*) s_)->recv (msg_, flags_));
 }
 
@@ -346,8 +373,10 @@ int zmq_poll (zmq_pollitem_t *items_, int nitems_, long timeout_)
     defined ZMQ_HAVE_HPUX || defined ZMQ_HAVE_AIX ||\
     defined ZMQ_HAVE_NETBSD
 
-    zmq_assert (items_);
-
+    if (!items_) {
+        errno = EFAULT;
+        return -1;
+    }
     pollfd *pollfds = (pollfd*) malloc (nitems_ * sizeof (pollfd));
     zmq_assert (pollfds);
     int npollfds = 0;
@@ -659,9 +688,10 @@ int zmq_errno ()
 
 int zmq_device (int device_, void *insocket_, void *outsocket_)
 {
-    zmq_assert (insocket_);
-    zmq_assert (outsocket_);
-    
+    if (!insocket_ || !outsocket_) {
+        errno = EFAULT;
+        return -1;
+    }
     switch (device_) {
     case ZMQ_FORWARDER:
         return zmq::forwarder ((zmq::socket_base_t*) insocket_,
@@ -735,7 +765,10 @@ unsigned long zmq_stopwatch_stop (void *watch_)
 {
     uint64_t end = now ();
     uint64_t start = *(uint64_t*) watch_;
-    zmq_assert (watch_);
+    if (!watch_) {
+        errno = EFAULT;
+        return -1;
+    }
     free (watch_);
     return (unsigned long) (end - start);
 }