Fixes bug where selection text and ammo graphic would disappear on failed unload
bin/data/Language/Polish.lng
fixing compilation errors on Linux

directory and file names are case sensitive!
std::cerr requires an #include
Merge pull request #273 from hmaon/seriously

fixing compilation errors on Linux
- Fixed not loading MIDIs properly.
- Fixed no error when audio files are missing.
- Fixed audio file priority (no longer need to delete GM.CAT).
- Fixed "mute" setting causing crashes.
WIP Controls stuff.
- Fixed used hangars miscounting crafts in production.
- Fixed misleading function name.
Fix map view of desert hills
Fix hidden aliens on top of slopes in map
fixing compilation errors on Linux

directory and file names are case sensitive!
std::cerr requires an #include
Merge remote-tracking branch 'upstream/master' into unloadTextFix
Merge pull request #272 from redx25/unloadTextFix

Minor inventory bug fix
Merge pull request #274 from radius75/Polish.lng

bin/data/Language/Polish.lng
Merge branch 'master' of https://github.com/SupSuper/OpenXcom