Fix for devdraw on MacOS 10.8 (Mountain Lion)

[robkroeger, 2012-07-31 12:19:11]

In MacOS 10.8, the NSBitmapImageRep class appears to cache the specified image
data at the time of construction. As a result updates to the backing memimage
object do not get pushed to the screen in flushimg.

This patch creates the NSBitmapImageRep object over again for each flushimg
which would appear to fix the problem.

[rsc, 2012-07-31 15:24:51]

*** Submitted as http://code.google.com/p/plan9port/source/detail?r=c89c9c245071
***

devdraw: fix for OS X 10.8 (Mountain Lion)

In MacOS 10.8, the NSBitmapImageRep class appears to cache the specified
image data at the time of construction. As a result updates to the
backing memimage object do not get pushed to the screen in flushimg.

This patch creates the NSBitmapImageRep object over again for each
flushimg which would appear to fix the problem.

R=rsc
CC=plan9port.codebot
http://codereview.appspot.com/6443063

Committer: Russ Cox <rsc@swtch.com>

[rsc, 2012-07-31 15:25:17]

Thanks very much! I haven't taken the time to upgrade yet, but I
confirmed that this works on Lion.