blakewatters/TransitionKit — pull request #17 by KATT (2014-02-26 14:15:34+00:00)
Title: Prevent adding a state which name is already persistent

Also keen on adding `addStateWithName:`, would you like me to add it?

Currently, I've implemented in a category, looking like this:
```objc
-(TKState*) addStateWithName:(NSString *)name
{
if (! [name isKindOfClass:[NSString class]]) [NSException raise:NSInvalidArgumentException format:@"Expected a `NSString` object, instead got a `%@` (%@)", [name class], name];

TKState *state = [TKState stateWithName:name];

[self addState:state];

return state;
}
```