Fixing an issue with stubs returning BOOL on 64bit iOS

Looks like on 64bit iOS `@encode(BOOL)` results in `B` instead of `c` (as in 32bit iOS and Mac OS as well as *surprise surprise* 64bit Mac OS).

Therefore `MKTSetReturnValueForInvocation` should have a dedicated check for `methodReturnType == @encode(BOOL)`.  
This check should be done after checking agains `@encode(char)` to not break char return types in non 64bit iOS.

Happy New Year
-ullrich

PS: I could reproduce this in my iOS7 only project, but unfortunately wasn't able to run the OCMockito test suite in 64bit, as my Xcode always decided to crash on trying so. I added a test for it anyway.