Two last freeze break requests: gnome-shell message tray

[Owen Taylor <otaylor redhat com>]

Two visual issues in the GNOME Shell message tray. Both purely
visual, but pretty safe patches.

A) Shows black blob when clicking on a notification to dismiss it
https://bugzilla.gnome.org/show_bug.cgi?id=645697#c5

Since a while ago, when you click on a message tray notification to 
activate it / dismiss it, we remove the notification immediately,
then fade the bubble away, resulting in a mysterious black blob
fade away on the screen. With recent changes to padding, this blob
became bigger and more obvious.

B) Sometimes notifications are ellipsized when expanding from the tray
https://bugzilla.gnome.org/show_bug.cgi?id=645719

We try to change a notification from "<subject> Body body body ..."
To "<subject>\nbody body body" using Mainloop.idle_add(), but we don't
actually reliably go idle during an animation, so the bubble pops
up ellipsized then at the end of the animation after it has eased
in place, reformats. Looks a bit odd.

[ Not going to promise these as the last freeze break requests, but
  they clear off my list; going to try to stick to crashers from this
  point forward :-) ]