We add PHP bindings for libgd's features to read and write BMP files, which
are available as of libgd 2.1.0.
As PHP's bundled libgd doesn't yet include the respective features of the
external libgd, we add these.
This initial checkin has no changes to any of the libgd code so it can
be used as a basis for diffs. It also will not build currently because
of this. The PHP gd checks need to be incorporated along with a bit of
other config magic. It also shouldn't break the build and will only
take effect if you use --with-gd=php right now.
