WINTERMUTE: Remove unused variables.
WINTERMUTE: Make BaseFileManager::registerPackages case agnostic.

The old version did only work as expected when all the filenames were all
lowercase. This seems to be the case for most (or even all?) WME games.
However, we are better safe than sorry and make the code case agnostic.
WINTERMUTE: Remove another unused variable.
WINTERMUTE: Slight interator usage cleanup.
WINTERMUTE: Use const_iterator in BaseFileManager::registerPackages.