Add filesystem case sensitivity detection

[bradallred]

See commit 0869613

Lots of platforms use case insensitive filesystems, and many have both as an option. Therefore the most sane thing to do is implement runtime detection.

We should probably just remove it from the config, tho we should measure if this check adds measurable overhead to file resolution (I doubt it).

We do need to keep in mind that gemrb and the data are possibly on separate filesystems.

[lynxlynxlynx]

I disagree, we should just detect it. It's simple to test.

[bradallred]

sure, I'll edit this to reflect that path.

[lynxlynxlynx]

I think three path groups will be enough. One for our files, one for game files and one for saves (more likely to be stored on a different partition, especially on ees). Then we can do three simple checks on startup and have almost no overhead in later calls. It would require more VFS API adjustments though. Any better ideas?