Overhauled the tracebox extending code, it now lives in collision.c rather than cl_co...

Overhauled the tracebox extending code, it now lives in collision.c rather than cl_collision.c/sv_phys.c and has 3 cvars controlling it:
collision_extendmovelength - affects ALL engine traces (physics, etc), this has a higher value because of how important it is to not get stuck in things.
collision_extendtraceboxlength - affects only the qc tracebox builtin.
collision_extendtracelinelength - affects only the qc traceline builtin (in particular it is a bad idea to set this to a high value because it can interfere with trace_inwater/trace_inair reporting).
Changed collision_enternudge/collision_leavenudge to behave more like Quake2/Quake3, this means that you can not sink into a brush (assuming the brush is detected - see collision_extendmovelength).
Some beautification on the RecursiveHullCheck and RecursiveLightPoint code.

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@12072 d7cf8633-e32d-0410-b094-e92efae38249
::stable-branch::merge=05441557527d65d14e141fbf7ae50c9bf11ae486