bug#17588: 24.3.91; mouse-face glitchy

[Christopher Schmidt <ch@ristopher.com>]

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    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.

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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