Added system check at start of selftests

- tests that system can provide at least 1,000 sockets
- we could expand on this but this covers the main case of OS/X
  having a too-low default limit of 256 handles per process

tests/test_system.cpp

@@ -0,0 +1,51 @@
+/*
+    Copyright (c) 2007-2013 Contributors as noted in the AUTHORS file
+
+    This file is part of 0MQ.
+
+    0MQ is free software; you can redistribute it and/or modify it under
+    the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    0MQ is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "../include/zmq.h"
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <unistd.h>
+#include <assert.h>
+
+//  This test case stresses the system to shake out known configuration
+//  problems. We're not using libzmq here but direct system calls. Note
+//  that code may need wrapping to be properly portable.
+
+int main (void)
+{
+    //  Check that we can create 1,000 sockets
+    int handle [1000];
+    int count;
+    for (count = 0; count < 1000; count++) {
+        handle [count] = socket (AF_INET, SOCK_STREAM, IPPROTO_TCP);
+        if (handle [count] == -1) {
+            printf ("W: Only able to create %d sockets on this box\n", count);
+            printf ("I: Tune your system to increase maximum allowed file handles\n");
+#if defined (ZMQ_HAVE_OSX)
+            printf ("I: On OS/X, run 'ulimit -n 1200' in bash");
+#elseif defined (ZMQ_HAVE_LINUX)
+            printf ("I: On Linux, run 'ulimit -n 1200' in bash");
+#endif        
+            return -1;
+        }
+    }
+    //  Release the socket handles
+    while (count)
+        close (handle [count--]);
+}