Added implementations for AtkObject:property-change support. Fixed some (but not...

Added implementations for AtkObject:property-change support.  Fixed some (but not all) ref counting bugs, and we now listen to selection-change events in simple-at.c.
Considerable rework in the event handling in the bridge and elsewhere.
Added Accessibility_Application_registerObjectEventListener(), which is used by the registry.
Worked around a logjam by omitting an unref() in event listeners, which probably means that there is now a memory leak... will keep investigating.
Mostly works but can still sometimes lock up on application exit if one leans on the app hard enough.

git-svn-id: http://svn.gnome.org/svn/at-spi/trunk@79 e2bd861d-eb25-0410-b326-f6ed22b6b98c