added Nexiuz TE_ effects (prefixed TE_TEI_) and Nexiuz plasma trail (an override...

added Nexiuz TE_ effects (prefixed TE_TEI_) and Nexiuz plasma trail (an override for EF_BRIGHTFIELD)
Nexiuz mode disables fullbrights
reshaped some of the particle structure (flags is gone, broken apart into separate fields again)
added tex_beam (which uses a separate texture instead of the particle font because it needs to repeat)
simplified some of the texture font generation (tex_ variables now indicate where to put the images in the texture)
now resets trail positions if entity was not active in previous frame
now gives packet dump when Host_Error is called during client message parsing code
now frees the model(s) being loaded when Host_Error is called during model loading code
removed modelflush command because it crashes the realtime lighting code (which points to leafs and surfaces in the world model, a problem which does not exist with r_restart and vid_restart)
R_Stain and R_CalcBeamVerts now use const where appropriate

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@2618 d7cf8633-e32d-0410-b094-e92efae38249