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