Previous versions of OS X seem to have automatically disabled
update for a window when flushing is disabled, but now we have to
do it ourselves, otherwise text editors can flicker a lot. (The
system change is probably related to the removal of the
`isFlushWindowDisabled` method of `NSWindow` (which was
deprecated in 10.10).
Allocation rules:
* Use `as-objc-allocation' when creating a Cocoa object. When the
resulting reference becomes unreachable, the Cocoa object will be
released.
* Use `with-autorelease' in atomic mode around calls that autorelease
and where the release should take effect immediate. Do not create
an autorelease pool except in atomic mode.
* Other autoreleased objects may end up in the root pool installed by
"pool.rkt". The root pool is periodically destroyed and replaced;
call `queue-autorelease-flush' if you need to encurage replacement
of the pool. If you need to use an object that might be autoflushed,
be sure that you're in atomic mode.
ea576d3177