Autofoo cleanups
Bring gtk-doc up to date.

It should build again and be properly included with make dist.

Based on nautilus-python changes, see below for the details.
https://git.gnome.org/browse/nautilus-python/log/docs?h=nautilus-3.0
Cleanup AM_CPPFLAGS
Don't set AC_PREFIX_DEFAULT
Fix distcheck so it works without root privilege