Make pak code more consistent.
* Added 'Pak_CloseFile' to SDK.
* Added partial rebuild of 'Pak_ProcessPakFile' to SDK.
* Added compile time assert for 'PakFileHeader_t' structure.
The min spec is SSSE3, using SSE4.1 instructions (_mm_extract_epi64) will break compatibility. The code containing the defect is debug only, and %90+ of the user base uses an SSE4.1 capable processor.
A mistake has been made, certain area's of the engine actually do allow strings larger than 128 bytes, just one routine that doesn't (console commands). Tokenizer only tokenizes it up to 512 bytes, so null all the other bytes past this. This still fixes the flaw mentioned in the comment at the place where the nulling happens.
