Merge pull request #582 from qehgt/fix-winsock-already-included

Fix 'WinSock.h has already been included' compiler error.

Author: redboltz

include/msgpack/sysdep.h

@@ -45,6 +45,9 @@
 
 #ifdef _WIN32
 #   define _msgpack_atomic_counter_header <windows.h>
+#   if !defined(WIN32_LEAN_AND_MEAN)
+#       define WIN32_LEAN_AND_MEAN
+#   endif /* WIN32_LEAN_AND_MEAN */
     typedef long _msgpack_atomic_counter_t;
 #   define _msgpack_sync_decr_and_fetch(ptr) InterlockedDecrement(ptr)
 #   define _msgpack_sync_incr_and_fetch(ptr) InterlockedIncrement(ptr)