This allows libcppa to compile and run on windows using g++ and MingW.

The examples and tests run. Remaining problems:
1. middleman_event_handler::update runs into "cannot erase " << ptr << " (no such element)" on disconnect of a remote actor.
2. chat example client crashes in windows on connect
backtrace just prints addresses.
added execinfo_windows.h for missing execinfo.h in mingw
uuid from disk partition now implemented.