bug#15899: 24.3.50; regression: `region' overlay is lower priority than default

[Drew Adams <drew.adams@oracle.com>]

> Isn't it confusing that the region highlighting is non-contiguous
> when an overlay is in its middle?

Yes.  And when a `face' or other display-related text property is
in its middle.  Or is at either end.  Or extends across the whole
region (which includes when the region is in the middle of a
stretch of highlighting).  I know from experience with the new
(and old) behavior.

Such situations are visually confusing to users.  And they can
complicate operating on text properties and, more generally,
using text properties and overlays.

This change should be reverted as soon as possible.  It is a
candidate for "What WERE they thinking?"  At the very least,
make such behavior optional for users (and certainly not the
default).

There are thousands of real bugs reported, many of them still
unresponded to.  There is no reason to spend time "fixing"
non-bugs such as this.  This should have gotten only a polite
"This is by design", perhaps followed by an explanation of why
the design (in Emacs and everywhere else!) is thus.