-The alpha blending functions should take alpha parameters in the range of 0 <= alpha <= 255 rather than <= 256. Although 256 represents fully-opaque, it overflows the blending functions. The higher-level drawing functions should test for full-opacity and change to the standard opaque column drawing functions instead, both to prevent overflows and for increased efficiency.

git-svn-id: http://odamex.net/svn/root/branches/rend32@3892 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Merge from trunk.

git-svn-id: http://odamex.net/svn/root/branches/rend32@3896 b0bcef46-2027-0410-bd56-ab726e9a1d04
-dc_textureheight should be set when rendering masked midtextures.

git-svn-id: http://odamex.net/svn/root/branches/rend32@3898 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Merge from trunk into rend32.

git-svn-id: http://odamex.net/svn/root/branches/rend32@3900 b0bcef46-2027-0410-bd56-ab726e9a1d04