Add UPnP support.

Feedback is in logs as suggested by skid_au. The checkbox is still there, but
mostly for people who would like to opt out (unfortunately, I can not be sure
how this feature may behave for some routers - there's a hell of a lot of bad
UPnP implementations.)

The Visual Studio stuff is a little messy, so I apologize if anything is a bit
off. I tested most configurations and it worked.

I also tested CMake on Debian Wheezy, Ubuntu Saucy, and Mac OS X Mountain Lion.
All seemed to be OK.

Externals/miniupnpc/src/miniwget.h

@@ -0,0 +1,30 @@
+/* $Id: miniwget.h,v 1.8 2012/09/27 15:42:10 nanard Exp $ */
+/* Project : miniupnp
+ * Author : Thomas Bernard
+ * Copyright (c) 2005-2012 Thomas Bernard
+ * This software is subject to the conditions detailed in the
+ * LICENCE file provided in this distribution.
+ * */
+#ifndef MINIWGET_H_INCLUDED
+#define MINIWGET_H_INCLUDED
+
+#include "declspec.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+LIBSPEC void * getHTTPResponse(int s, int * size);
+
+LIBSPEC void * miniwget(const char *, int *, unsigned int);
+
+LIBSPEC void * miniwget_getaddr(const char *, int *, char *, int, unsigned int);
+
+int parseURL(const char *, char *, unsigned short *, char * *, unsigned int *);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+