[ft] Autohinting and monospaced fonts

[Weeble]

I've been looking into a problem experienced by a Pygame user when
trying to work with certain monospaced fonts, where it was observed
that different glyphs varied in width by up to 2 pixels. Pygame uses
SDL_ttf which in turn uses FreeType for handling text rendering.

You can see the discussion and investigation where it was reported
here: https://bugs.launchpad.net/ubuntu/+source/ttf-freefont/+bug/1001033

As far as I can tell, the problem only appears in FreeType version
2.4.5 and later, because old versions detected monospaced fonts and
forced the advance width of all glyphs to advance_Width_Max. As I
understand it, this behaviour was removed in commit
8c82ec5b17d0cfc9b0876a2d848acc207a62a25a due to problems with CJK
fonts.

Also, it only occurs in certain fonts. It affects the FreeMono in this bundle:

http://ftp.gnu.org/gnu/freefont/freefont-ttf-20100919.tar.gz

but not the one in this bundle:

http://ftp.gnu.org/gnu/freefont/freefont-ttf-20090104.tar.gz

I think perhaps one includes hinting information and the other
doesn't? I'm not sure there.

Is this expected? Should autohinting on a monospaced font result in
some glyphs having different advance widths? It seems surprising, but
to be honest I don't know an awful lot about text rendering, so I'm
not sure what to expect.