[Libguestfs] RHSrvAny: Fix failure on Windows 2003

[Matthew Booth]

The newly rebuilt RHSrvAny worked on Windows XP, Windows 2003 R2, and Windows
Vista+, but segfaulted on Windows 2003. After much investigation, the issue
seems to have been with inconsistent use of Unicode.

This series fixes compilation on Microsoft Visual C++ 2010 (the most recent
version which runs on Windows 2003), fixes all compiler warnings, and enabled
warnings during the build. The resulting executable now works on Windows 2003
both when built by MSVC 2010 and mingw32 on F19.

Matt