force shadowmapping when deferred rendering is on

force shadowmapping when deferred rendering is on
reworked lighting code a bit to ensure consistent behavior
fixed multiple bugs with r_ambient, .colormod, r_fullbright,
r_shadow_gloss 2, and other lighting parameters
overhauled GLSL shader to ensure consistency
fixed bug with deferred rendering of polygonoffset on submodels
deferred rendering path now checks for transparent surfaces and uses the
forward rendering path on them

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@9594 d7cf8633-e32d-0410-b094-e92efae38249