[MP] Improve cvar code a bit further.  Based mostly on zturtleman/spearmint@778bce425a2e6b6860e9d5ec4c7fc736311f9351.
With some changes for legacy support still (and extra cvars that should be allowed in mods, if the mods were incorrectly setting them).
And also some other misc stuff related to OpenJK specific.
[MP] Use bsearch for cg_spawn.c
[MP] Fix double spawn effect on siege respawns.
[MP] g_saga.c unneeded tent pointer.
Merge branch 'master' into rend2