GtkTreeView: stop ignoring crossing events from grabs

GtkTreeView: stop ignoring crossing events from grabs

Stop ignoring various crossing events from grabs:

Enter events with type GRAB/GTK_GRAB/GTK_UNGRAB/STATE_CHANGED:
  Ignoring these events was added as a workaround for synthesized
  events not having the right coordinates (see bug 555109) but
  now they do have the right coordinates. (see bug 704456)

Leave events with types types GTK_GRAB/GTK_UNGRAB:
  Ignoring these events was added because since we were ignoring
  the enter events as above, ignoring the leave events meant we
  could lose the prelighted row in a grab-triggered leave/enter
  pair. (See bug 653676. It's also now impossible to
  reproduce the leave events that were reported in that bug as causing
  problems.)

Leave events of type GRAB.
  Ignoring these events was added without a ChangeLog entry in 2001,
  possibly to keep the prelight from flashing when activating menus.
  But ignoring these events could lead to stuck prelighting, and we don't
  do it for any other widgets.

https://bugzilla.gnome.org/show_bug.cgi?id=726209

The bug this patch is fixing is that currently if you have a GtkPopover in
clicking off the popover to dismiss it on a GtkTreeView (which triggers
a synthetic enter event on the GtkTreeView) will leave the GtkTreeView
in a confused state until the user moves the mouse again.