Amend gcin.spec to handle the immodules cache.

From 'rpm -q --scripts gcin', %gtk{2,3}_immodule_postun only updates
the immodules cache for uninstall:

if [ $1 -eq 0 ]; then
/usr/bin/gtk-query-immodules-2.0 > /etc/gtk-2.0/gtk.immodules
fi

This may cause the inconsistent immodule cache after package upgrade.
($1 == 1 in upgrade)

I follow the script in gtk2.spec and gtk3.spec to update the immodule
cache to avoid the inconsistent cache.