Various MinGW compile fixes.
Merge pull request #394 from dpogue/mingw-fixes

Various MinGW compile fixes.
Clean up some warnings, and make the CRT ones more relevant
Added link to Roadmap wiki page.
Fixes for semaphores on *nix.
Remove plFileSystem::GetTempFileName.

It was unused and on *nix used the deprecated mktemp function.
Fix a clang warning in plPythonPack.
Merge pull request #393 from dpogue/nix-fix

*nix fixes
Merge pull request #397 from zrax/warnings

Clean up some warnings, and make the CRT ones more relevant