Fix that executing applescript may hang emacs uninterruptedly.

Fix that executing applescript may hang emacs uninterruptedly.

* nsfns.m (as_script, as_result, as_status): New static variables.
(ns_run_ascript): New function.
(Fns_do_applescript): Set variables as_*. Make an NSApplicationDefined
event with data2 set to NSAPP_DATA2_RUNASSCRIPT, post it and then start
the event loop.  Get status from as_status.

* nsterm.h (ns_run_ascript): Declare.
(NSAPP_DATA2_RUNASSCRIPT): Define.

* nsterm.m (sendEvent): If event is NSApplicationDefined and
data2 is NSAPP_DATA2_RUNASSCRIPT, call ns_run_ascript and then exit
the event loop (Bug#7276).