Fix jk2 caching system

[aufau]

JK2 caches many resources and tries to reuse them on fs module reinitialisation (behaviour not present in original q3 engine). These are for example shaders, .sp files, models, map data etc. The issue is that it fails to invalidate cache in most scenarios, which becomes apparent when changing server/mod without restarting jk2 client.

It may be impossible/very hard to fix it without removing the cache system altogether, but in 2018 I think we could give away some performance for correctness considering how fast the game runs anyway.

[ouned]

yeah I think removing it would be the best solution