support for Linux-native studiomdl

[JJL772]

Some games like Momentum Mod and Portal 2: Community Edition ship a Linux-native version of studiomdl. This PR adds support for Linux-native studiomdl if it exists.

Summary of changes:

• Check for studiomdl instead of only studiomdl.exe
• Rework some of that bin directory finding code
• Don't re-resolve bin directory if game directory didn't actually change (this was mainly just an annoyance for me when dealing with non-standard modelsrc,etc paths)

I wasn't able to test this on Windows yet, just opening for preliminary review I guess

[bonjorno7]

Oh thanks! I'll review it tomorrow and test on windows.

[bonjorno7]

@JJL772 The force push makes it kind of confusing to review but I'll try.

[JJL772]

@bonjorno7 Sorry for the force push! Totally forgot about this PR until now- is there anything else you want me to do here?

[bonjorno7]

It's been 10 months and I've completely forgotten what this is about lol