Log Message:
Move "configuration" files from PKG_SYSCONFDIR to PREFIX/libdata.  Those
files are not intended to be configured by the end user, but should be
automatically regenerated when (de)installing extra GTK modules.
Bump PKGREVISION to 3 because of this change.

While doing this, implement a framework so that other packages installing
GTK modules can rebuild those databases easily at (de)install time.