added gl_mesh_batching (default on) which merges several meshes in a row to reduce...

added gl_mesh_batching (default on) which merges several meshes in a row to reduce overhead of array locking and drawing
added MESH_VAR and MESH_BATCH defines to allow relevant code to be disabled (MESH_VAR is currently disabled because it's somewhat broken last I checked)
added custom array pointer support in R_Mesh_State (MainState and TextureState), this is experimental but works fine
added gl_mesh_copyarrays (default off) which tells renderer code that it should use custom array pointer support instead of copying (currently testable on surface rendering - not a good use, too many Pointer calls for very little geometry)
some other cleanups

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@3019 d7cf8633-e32d-0410-b094-e92efae38249