Disable the auto-affinity code, which pinned warsow process to a single core

Served as a workaround to NV's threaded optimization, which was ok in the time when warsow was a single-threaded app.
Make Com_Printf thread-safe
Make memory allocation functions thread-safe
Make the most commonly used FS functions thread-safe

This commit slightly changes semantics of how FS_ functions work on curl streams but hopefully it won't wreak any havoc
Make wswcurl thread-safe, remove blocking wswcurl_perform calls
Move background track loading code into a separate thread
Some loading screen code refactoring
Fix an oopsie