add introspection into GTK libs (part of #517)

This is all work of Marc Weber <marco-oweber@gmx.de>, except for a few nitpicks.

Tested space blowup: IMHO negligible to headers and similar stuff,
e.g. the firefox closure (reported by du) grows from 560 to 579 MB.
Saving space should be handled separately,
e.g. we have the multiple-outputs branch.
disable auto-detected introspection for libwnck and clutter

Didn't build as it was, and not needed anywhere AFAIK.
introspection disabling -- clutter-gtk, NM-applet, gnome_panel

Didn't build as it was, and not needed anywhere AFAIK.
qt, glew: propagate glu

After removing qt's dependency on the symlinked combination of mesa and glu,
many qt apps were missing it now (since e9f0d10).
I resove this to a compromise.
mesa: attempt to fix driverLink on darwin
introspection disabling -- libchamplain

Didn't build as it was, and not needed anywhere AFAIK.
darwin: attempt to fix pango via flattening cairo includes

Changes hash only on darwin.