tests/glibmm_refptr: Add simpler tests for move constructor/operator=.
tests/glibmm_refptr: Add simpler tests for move constructor/operator=.

The *with_parent* tests test much the same thing, but these ones
are simpler, based on Marcin Kolny's simpler tests for the
universal reference versions.

GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,GNOME/glibmm