-Replace R_DrawParticleP and R_DrawParticleD with a simplified version for both.
-Add a span drawing function R_FillTranslucentSpan primarily for drawing the rows of particles.

git-svn-id: http://odamex.net/svn/root/branches/rend32@3939 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Add a y1 and y2 field to vissprite_t to save the min and max values of a sprite's Y projection onto the screen.
-Change R_DrawParticle to use vissprite_t::y1 and y2.

git-svn-id: http://odamex.net/svn/root/branches/rend32@3940 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Fix a sprite clipping bug that caused 2-sided segs that completely fill the remainder of a screen column to be ignored when clipping sprites behind the seg.

git-svn-id: http://odamex.net/svn/root/branches/rend32@3941 b0bcef46-2027-0410-bd56-ab726e9a1d04