Fix socket creation above sistem limits for all 'other' OS not covered by…

Fix socket creation above sistem limits for all 'other' OS not covered by eventfd, windows or vms; enhanced test to create sockets up to a bigger limit to really test hitting the OS limit

src/signaler.cpp

@@ -474,7 +474,7 @@ int zmq::signaler_t::make_fdpair (fd_t *r_, fd_t *w_)
     int rc = socketpair (AF_UNIX, SOCK_STREAM, 0, sv);
     if (rc == -1) {
         errno_assert (errno == ENFILE || errno == EMFILE);
-        sv [0] = sv [1] = -1;
+        *w_ = *r_ = -1;
         return -1;
     }
     else {

tests/test_many_sockets.cpp

@@ -22,13 +22,14 @@
 #include <stdio.h>
 #include <stdlib.h>
 
-const int no_of_sockets = 5000;
+const int no_of_sockets = 2 * 65536;
 
 int main(void)
 {
     setup_test_environment();
 
     void *ctx = zmq_ctx_new();
+    zmq_ctx_set(ctx, ZMQ_MAX_SOCKETS, no_of_sockets);
     void *sockets[no_of_sockets];
     
     int sockets_created = 0;