[Fontconfig] 2.4 preparations

[Matthias Clasen]

One thing that would be great to change for 2.4
is to ship pre-generated documentation in the tarball,
and have a --disable-docs configure option to avoid
regenerating the docs when installing from the tarball.

This is generally accepted best practice, and avoids
a lot of fragile build-time dependencies on jade, tex,
sgml tools, etc. I am currently having problems building
fontconfig in rawhide, because jade has problems on ppc.
This should not be necessary at all unless the docs
are platform-dependent.

Matthias