take in (id)block as (void (^)())block so that bindings from MonoTouch work properly.

I was trying to use MBAlertView from a MonoTouch project and I get runtime SIGSEGV crashes. I asked the Xamarin guys to look into it and it turns out that taking in blocks as id causes this problem. See here for more information: http://forums.xamarin.com/discussion/comment/4208#Comment_4208