bug#17588: 24.3.91; mouse-face glitchy

[Christopher Schmidt]

    emacs -q
    M-: (run-at-time nil 0.01
                     (lambda ()
                       (with-current-buffer (get-buffer-create "rms")
                         (with-silent-modifications
                           (dotimes (_ 10)
                             (insert (if (= (random 2) 1) "gpl" "fsf") "\n")))
                         (when (> (- (point-max) (point-min)) 100)
                           (delete-region (point-min) (+ (point-min) 100)))))) 
RET
    C-x 2
    C-x 3
    C-x b rms RET
    C-x o
    C-x b rms2 RET
    C-x o
    C-x b rms2 RET
    M-: (dotimes (i 1000)
          (insert (propertize (format "%3d%3d%3d" i i i)
                              'mouse-face 'highlight)
                  "\n")) RET
    # Move your mouse pointer around within the rms2 windows and the
    # modeline of the rms window.

I see two glitches with regard to mouse-face highlighting.  Either there
is no highlighting at all or the font does not switch back to the
regular one after leaving the connected highlight region.

This recipe is not exactly reliable.  It usually takes up to 20 seconds
of mouse movement to trigger the issue here.  Some scrolling helps.

I realise my recipe puts a lot of pressure on the display engine.  When
reducing the timer's REPEAT value, the issue does not vanish but is
harder to reproduce.  My real use-case, which provokes this issue after
a few minutes, is a process filter which updates the buffer of a window
exactly once a second.

When applying this recipe to 24.3 on the same system using the same
libraries for building the binary, there are some glitches.  Most
notably the mouse face of mode-line-buffer-identification is not reset
reliably.  Yet 24.3.91 is a lot worse than 24.3.  IMO this is a
regression.

    In GNU Emacs 24.3.91.3 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.10)
    Repository revision: 117154 eliz@gnu.org-20140525141846-w6719v7ajcd3tbkk
    Windowing system distributor `The X.Org Foundation', version 11.0.11204000