patch: fix WSARecv invocation; report WSA errors

[Denis Bilenko]

WSARecv() sometimes fails with WSAEFAULT if lpFlags parameter is zero.
See comment at the end of this page:
http://msdn.microsoft.com/en-us/library/windows/desktop/ms741688%28v=vs.85%29.aspx

The patch below fixes that. It also reports errors to stderr so that
bugs like this are easier to catch in the future.

--- /home/denis/work/libev-cvs/ev.c	2012-05-10 20:47:37.064383729 +0400
+++ libev/ev.c	2012-05-12 01:36:54.925647219 +0400
@@ -1880,7 +1880,17 @@
           DWORD sent;
           buf.buf = &buf;
           buf.len = 1;
-          WSASend (EV_FD_TO_WIN32_HANDLE (evpipe [1]), &buf, 1,
&sent, 0, 0, 0);
+          if (WSASend(EV_FD_TO_WIN32_HANDLE (evpipe [1]), &buf, 1,
&sent, 0, 0, 0))
+            {
+              int error;
+              error = GetLastError();
+              if (error != WSAEWOULDBLOCK)
+#if EV_AVOID_STDIO
+                ev_printerr ("(libev) WSASend failed.\n");
+#else
+                fprintf(stderr, "(libev) WSASend failed with error
%d\n", error);
+#endif
+            }
 #else
           write (evpipe [1], &(evpipe [1]), 1);
 #endif
@@ -1912,9 +1922,22 @@
 #ifdef _WIN32
           WSABUF buf;
           DWORD recvd;
+          DWORD flags;
           buf.buf = dummy;
           buf.len = sizeof (dummy);
-          WSARecv (EV_FD_TO_WIN32_HANDLE (evpipe [0]), &buf, 1,
&recvd, 0, 0, 0);
+          flags = 0;
+          if (WSARecv(EV_FD_TO_WIN32_HANDLE(evpipe[0]), &buf, 1,
&recvd, &flags, 0, 0))
+            {
+              int error;
+              error = GetLastError();
+              if (error != WSAEWOULDBLOCK)
+#if EV_AVOID_STDIO
+                ev_printerr ("(libev) WSARecv failed.\n");
+#else
+                fprintf(stderr, "(libev) WSARecv failed with error
%d\n", error);
+#endif
+            }
+
 #else
           read (evpipe [0], &dummy, sizeof (dummy));
 #endif