Add build command, to build single extensions easily
nemo-preview: Add hidpi support.  This is slightly flaky because I don't think
GtkClutterEmbed has 100% hidpi support yet.  It works fine, though occasionally
you may get an out of position clutter stage briefly, which mouse-overing seems
to fix.
Do a relayout after everything is loaded... seems to help some with
positioning the stage right within the gtk window