bug#23924: 25.1.50; Emacs NSInternalInconsistencyException on macos Sierra developer beta 2

[Bob Halley]

If I disable the invocation of nextEventMatchingMask:untilDate:inMode:dequeue 
at nsterm.m:3950, the problem stops.  And indeed, this is the method that is 
called in the traceback that is causing the assertion to fire.  Since this 
appears to be a workaround for events getting eaten, however, this doesn't seem 
to be a good fix.

Is it a bad thing to just always set send_appdefined=YES?  The code appears to 
be trying to suppress appdefined events in some cases, but it's not clear to me 
what happens if we stop trying to send only one.  Naively I'd think "why not, 
so the run loop gets stopped twice, it's a little extra work" but I don't know 
this code and am not familiar with the macOS API :)