pkp: po alternative to lookup via valueForKeyPath:

pkp is a command to print out a key path.   LLDB has pretty bad . notation resolution, especially through (id) return results, so I've been using [self valueForKeyPath:@"whatever.keypath.failed.inlldb"] to work around this.   This helper makes that very easy!


![screen shot 2014-11-20 at 4 23 12 pm](https://cloud.githubusercontent.com/assets/114322/5133252/a0690ece-70d1-11e4-86b4-3a9549e818a0.png)




The use of `self` here is misleading. To offer a possible wording:

> Print out the value of the key path expression using `-valueForKeyPath:`.