Fix crash passing blocks to a mock method

The purpose of this patch is fixing a EXC_BAD_ACCESS crash that occurs after running a test in which an inline block capturing a scope variable is passed as a method argument to a mock.

Example:
```
NSString *someVariable = @"hi";
MyClass *object = mock([MyClass class]);
[mock someMethodWithBlock:^{
    [someVariable doSomething];
}];
```
With a Deployment Target of iOS 5, the blocks are not copied, and therefore when the captured arguments are released, this block in the stack gets released more times than it should.