GtkModule fixes

[Owen Taylor <otaylor redhat com>]

> > 56916 GtkModule fixes
> >   Notes:    Tim should look at what I put in the bug description.
> >             Seems to barely count as API issues.
> >   Puntable: 
> >   Breakage: Some
> >   Time:     1 hour
> 
> this is really a small issue. all that's involved is someone implementing
> code and Makefile.am stubs to:
> - let gtk figure a gtk-specific directory in configure.in into which
>   custom modules can install themselves

The directory should probably be:

 $libdir/gtk-2.0/GTK_MAJOR.GTK_MINOR.(GTK_MICRO - GTK_BINARY_AGE)/modules

Currently, we are installing input-method modules (which are third-party
addable) and pixbuf loaders (which aren't) in 

 $libdir/gtk-2.0/GTK_MAJOR.GTK_MINOR.GTK_MICRO/{immodules,loaders}

But those could be changed to be in (GTK_MICRO - GTK_BINARY_AGE) as well.

> - search that gtk-specific module directory for modules passed in through
>   GTK_MODULES= in gtk_main()
> - put GtkModuleDir=... into gtk-2.0.pc
> - implement means in pkg-config so custom module installers can do
>   pkg-config --get-variable=GtkModuleDir gtk-2.0
>   (or maybe pkg-config has such a thing already, dunno)

Yes, it already has such a thing:

$ pkg-config --help
[...]
  --variable=VARIABLENAME                        get the value of a variable

The one issue here is the one of "packages should not install outside there
own prefix". How does a user install GLE in /opt if GTK+ is installed 
in /usr, and /usr mounted read-only?

Regards,
                                        Owen