Add clutter_get_current_event

When getting signals from higher level toolkits, occasionally
one wants access to the underlying event; say for a Button
widget's "clicked" signal, to get the keyboard state.

Rather than having all of the highlevel widgets emit
ClutterEvent just for the more unusual use cases,
add a global function to access the event state.

http://bugzilla.openedhand.com/show_bug.cgi?id=1888

Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>

doc/reference/clutter/clutter-sections.txt

@@ -977,6 +977,7 @@ clutter_input_device_get_device_type
 
 <SUBSECTION>
 clutter_get_current_event_time
+clutter_get_current_event
 
 <SUBSECTION Standard>
 CLUTTER_TYPE_EVENT