Consider face inheritance when checking region face background.

Consider face inheritance when checking region face background.

Some themes (like dracula) make the region face inherit from some
other face.  If the background color of the region was inherited,
`indicate-copied-region' did the switch-point-and-mark-twice dance
which is not visible in case the region is highlighted.  It just
looked like Emacs would hang for a second after M-w.

* lisp/simple.el (indicate-copied-region): Consider face inheritance
when checking region face background.