dist tarballs shouldn't ever be released without the documentation,
and this allows us to build the tarballs with pre-generated docs
that get installed on the end system, but don't need to be built
there. So the end system doesn't need gtk-doc installed, only
the dist system does.
https://bugzilla.gnome.org/show_bug.cgi?id=700093
Use --enable-doc and --enable-tests instead of --with-docs and
--with-tests. This is consistent with other features and with
--enable-gtk-doc option. Support current variants as fallback.
Don't build tests unless --enable-tests is specified.
0.7 requires dbus 1.1 or greater (for system bus activation), so make that
explicit, and remove compat code for D-Bus 0.6 and earlier. Consolidate
the various glib pkgconfig checks into one, since most anything will require
gthread, glib, and gobject anyway. Fixup the docs makefile to be more
automake-compatible and let 'make clean' actually work correctly when
docs are built.
