-Break R_ClipLine apart into R_ClipLineToFrustum, R_ProjectPointX, R_ProjectPointY, R_CheckProjectionX and R_CheckProjectionY and move them into r_main.cpp.
-R_ClipLineToFrustum uses double-precision floating-point calculations for now as it seems to help with preventing overflows that led to HOMs in R_CheckBBox in some situations.
-Rewrote R_ProjectSprite and R_ProjectParticle to use these functions.
-Modify R_PrepWall to eliminate lclip1 and lclip2. Instead, R_PrepWall accepts the clipped line endpoints.

git-svn-id: http://odamex.net/svn/root/branches/rend32@3704 b0bcef46-2027-0410-bd56-ab726e9a1d04