added r_batch_multidraw and r_batch_multidraw_mintriangles cvars, this

added r_batch_multidraw and r_batch_multidraw_mintriangles cvars, this
code defaults on, restoring the old rendering path that used multiple
glDrawRangeElements calls for surface batching rather than copying index
data, on high poly maps this has a positive impact, on low poly maps I
was unable to find a difference in fps either way

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@11871 d7cf8633-e32d-0410-b094-e92efae38249
::stable-branch::merge=f08475bfc84f81a7563982fb4599c75977e7a00e