migrate OS X from NSAutoreleasePool to @autoreleasepool

Offending files found via:
$ find . -type f -name '*.h' -o -name '*.cpp' -o -name '*.mm' -o -name '*.m' -exec grep -l "NSAutoreleasePool" {} \;

While it would appear as though a lot of code has changed, really it is largely due to an extra level of indentation required by @autoreleasepool. Additionally, all lines touched should be normalized to use tabs instead of spaces - I'm not a fan of tabs, but I'd rather be consistent than not.

One API change made in ofSystemAlertDialog() to migrate off a mega deprecated NSAlert API.

One file was updated that targets iOS, seemingly missed in #2888.
fix compile error due to variable scope

The width and height variables are used outside the Autorelease Pool Block, oups. Indentation within the block scope was also sorted to be consistent with the method.
Merge pull request #3058 from pizthewiz/osx-autoreleasepool

migrate OS X from NSAutoreleasePool to @autoreleasepool