[analyzer] Check for +raise:format: on subclasses of NSException as well.

We don't handle exceptions yet, so we treat them as sinks. ExprEngine
hardcodes messages that are known to raise Objective-C exceptions like -raise,
but it was only checking for +raise:format: and +raise:format:arguments: on
NSException itself, not subclasses.

<rdar://problem/11724201>

llvm-svn: 159010