Default HWMs are set to 1000

This patch is meant to prevent users from running out of memory
when using 0MQ in the default configuration.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

doc/zmq_getsockopt.txt

@@ -81,12 +81,10 @@ blocking or dropping sent messages. Refer to the individual socket descriptions
 in linkzmq:zmq_socket[3] for details on the exact action taken for each socket
 type.
 
-The default 'ZMQ_SNDHWM' value of zero means "no limit".
-
 [horizontal]
 Option value type:: int
 Option value unit:: messages
-Default value:: 0
+Default value:: 1000
 Applicable socket types:: all
 
 
@@ -103,12 +101,10 @@ blocking or dropping sent messages. Refer to the individual socket descriptions
 in linkzmq:zmq_socket[3] for details on the exact action taken for each socket
 type.
 
-The default 'ZMQ_RCVHWM' value of zero means "no limit".
-
 [horizontal]
 Option value type:: int
 Option value unit:: messages
-Default value:: 0
+Default value:: 1000
 Applicable socket types:: all
 
 

doc/zmq_setsockopt.txt

@@ -38,12 +38,10 @@ blocking or dropping sent messages. Refer to the individual socket descriptions
 in linkzmq:zmq_socket[3] for details on the exact action taken for each socket
 type.
 
-The default 'ZMQ_SNDHWM' value of zero means "no limit".
-
 [horizontal]
 Option value type:: int
 Option value unit:: messages
-Default value:: 0
+Default value:: 1000
 Applicable socket types:: all
 
 
@@ -60,12 +58,10 @@ blocking or dropping sent messages. Refer to the individual socket descriptions
 in linkzmq:zmq_socket[3] for details on the exact action taken for each socket
 type.
 
-The default 'ZMQ_RCVHWM' value of zero means "no limit".
-
 [horizontal]
 Option value type:: int
 Option value unit:: messages
-Default value:: 0
+Default value:: 1000
 Applicable socket types:: all
 
 

src/options.cpp

@@ -24,8 +24,8 @@
 #include "err.hpp"
 
 zmq::options_t::options_t () :
-    sndhwm (0),
-    rcvhwm (0),
+    sndhwm (1000),
+    rcvhwm (1000),
     affinity (0),
     rate (100),
     recovery_ivl (10000),