-Eliminate a few warnings.

git-svn-id: http://odamex.net/svn/root/branches/texmanager@4370 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Use decrementing counters in the SSE2 drawing functions.
-Fix a bug calculating 16-byte alignment counters in the SSE2 drawers.

git-svn-id: http://odamex.net/svn/root/branches/texmanager@4374 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Change the shading functors in r_draw.cpp to return a the shaded color rather than writing to the address pointed to by dest.
-Remove checks for 0 count columns in the drawing functions and change the inner loop to a while loop instead of do while.

git-svn-id: http://odamex.net/svn/root/branches/texmanager@4375 b0bcef46-2027-0410-bd56-ab726e9a1d04