-Change particle projection to be similar to sprite projection and clipping.
-Make the const NEARCLIP global so it can be reused by sprite and particle clipping.
-Re-order the sprite clipping to hopefully reject out-of-view sprites sooner and more efficiently.

git-svn-id: http://odamex.net/svn/root/branches/persdiv@3661 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Factor the line clipping code out of R_AddLine into its own function R_ClipLine.

git-svn-id: http://odamex.net/svn/root/branches/persdiv@3662 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Change R_PointOnSide and R_PointOnSegSide to use vector cross-products to calculate the result.

git-svn-id: http://odamex.net/svn/root/branches/persdiv@3663 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Fix a bug calculating lclip1 for clipping linesegs in R_ClipLine.
-Round x1 and x2 before truncating in R_ProjectSprite and R_ProjectParticle.

git-svn-id: http://odamex.net/svn/root/branches/persdiv@3664 b0bcef46-2027-0410-bd56-ab726e9a1d04