com_hunkmegs replacement

[ouned]

dynamically requesting memory makes more sense in 2016.
https://github.com/JACoders/OpenJK/blob/master/codemp/qcommon/z_memman_pc.cpp

[aufau]

They replaced hunk memory with zone memory tagged by TAG_HUNK. I'd like to have a list of all reasons for id tech 3 using hunk memory before dropping it.

• Bad performance/buggy malloc on DOS (obsolete)
• Performance – hunk memory is often used for large number of small, dynamic-like allocations.
• Leak safety – hunk permanent memory is normally dropped only when unloading a map so there is no Hunk_Free and leaking possibility. (zone memory can do as well with Z_FreeTags)
• HUNK_DEBUG (hunklog, hunksmallog). I actually used it for debugging.
• Deterministic memory layout – This allows us to consistently reproduce memory bugs.
• …more?

To me these reasons are enough to keep it. Perhaps we could automatically adjust com_hunkmegs to improve on the original issue.