New payload meterpreter reverse_https_proxy

This payload is a variation on the reverse_https payload.

It allows you to specify a custom proxy IP and port, 
and all http/https traffic will be forced to use that proxy,
regardless of the system proxy settings.

Will post test results in a few moments.

Note : I have compiled metsrv.dll with MS Visual C++ 2010 Express. 
The binary appears to be smaller, but works well.
If you're cautious about using the dll in this PR, feel free to recompile.
Changes to server_setup.c are part of this PR, so this should be trivial.