Fix memory management for static block variables in UIAlertView+MKBlockAdditions

[albertodebortoli]

If objects referenced in the blocks are deallocated, in the next invocation of alertViewWithTitle:message:cancelButtonTitle:otherButtonTitles:onDismiss:onCancel: block arguments still reference to deallocated instances causing crash.
Fix the case if more than one UIAlertView is shown using block-based category method.
Add thread safety.

[drewish]

I'm getting errors on these lines:

UIAlertView+MKBlockAdditions.m:108:6: Use of undeclared identifier '_cancelBlock'
UIAlertView+MKBlockAdditions.m:109:5: Unknown type name '_cancelBlock'; did you mean 'CancelBlock'?

[drewish]

I think that should probably be:

[alertView.cancelBlock release];
alertView.cancelBlock = nil;
[alertView.dismissBlock release];
alertView.dismissBlock = nil;

[drewish]

Yeah so it looks like pull request #7 made those into dynamic properties. I'm not sure if your change is still necessary but it should probably become something more like what I showed above.

[drewish]

Okay I rebased your commit and fixed that: drewish@1994aa5