-Remove the seg_t* parameter from R_PrepWall since curline can be used instead.
-Use the linedef's endpoint instead of the seg's endpoint for texture column calculation for a small improvement in accuracy. There are still some texture alignment issues.

git-svn-id: http://odamex.net/svn/root/branches/rend32@3705 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Fix a bug calculating a sprite's offset when it is clipped at the left screen edge.

git-svn-id: http://odamex.net/svn/root/branches/rend32@3706 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Reject lines in R_ClipLineToFrustum that are completely off the left or right edges of the screen.

git-svn-id: http://odamex.net/svn/root/branches/rend32@3707 b0bcef46-2027-0410-bd56-ab726e9a1d04