-Don't add Z_Close to the list of functions to call at exit since it's already called via D_Shutdown.

git-svn-id: http://odamex.net/svn/root/branches/texmanager@4357 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Remove length, lengthstep, and texture offset from drawseg_t. These are replaced with uinvz1, uinvz2, and uinvzstep.
-Fixes a bug when clipping the length of a texture that is visible through an opening, producing textures that appear to stretch or compress.

git-svn-id: http://odamex.net/svn/root/branches/texmanager@4358 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Add operations to perform fixed-point multiplication and division between numbers of differing precision and convert the result to an arbitrary precision.
-Add invz1, invz2, and invzstep fields to drawseg_t to store the inverse of the distance to the first column and last column.
-Use drawseg_t::invz1 and invz2 to calculate texture mapping coordinates for drawing wall segs.

git-svn-id: http://odamex.net/svn/root/branches/texmanager@4359 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Calculate z from mInvZ in SegTextureMapper and multiply by z instead of dividing by 1/z when calculating the texture coordinates and scaling for wall segment columns.

git-svn-id: http://odamex.net/svn/root/branches/texmanager@4360 b0bcef46-2027-0410-bd56-ab726e9a1d04