Couple of minor issues in MSVC build fixed

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

src/pgm_socket.cpp

@@ -682,7 +682,7 @@ int zmq::pgm_socket_t::compute_sqns (int tpdu_)
     if (sqns == 0)
         sqns = 1;
 
-    return sqns;
+    return (int) sqns;
 }
 
 #endif

src/tcp_socket.cpp

@@ -93,7 +93,7 @@ int zmq::tcp_socket_t::write (const void *data_, size_t size_)
     return (size_t) nbytes;
 }
 
-int zmq::tcp_socket_t::read (void *data_, size_t size)
+int zmq::tcp_socket_t::read (void *data_, size_t size_)
 {
     int nbytes = recv (s, (char*) data_, (int) size_, 0);