Install doc-install.pl so that older mm modules can find it (#740790)
Requested by the ARM people. Instead of backporting fixes to various
modules that are looking for doc-install.pl in the wrong place
(gconfmm26, goocanvasmmm, gtkmm24, libvtemm), just ship it in glibmm24
as a temporary workaround in F15.
https://bugzilla.redhat.com/show_bug.cgi?id=740790