+ Gets installed
+ Uses a helper tool, gst-completion-helper, installed in
bash-completions/helpers.
+ Adds a common script that other tools can source.
https://bugzilla.gnome.org/show_bug.cgi?id=744877
and install into a different directory $(libexecdir/gstreamer-0.10) so that
everything is versioned properly.
NOTE: run 'make clean' after updating; if you are running an uninstalled setup,
you will need to update your gst-uninstalled script (unless it's symlinked
to gstreamer core master) and exit/enter your uninstalled environment to get
the updated environment. If you are running an installed setup, you should
run 'make uninstall' before merging this change or remove the old
plugin-scanner binary manually.
Fixes#601698.