PonyDebugger uses CoreGraphics

PonyDebuger uses CGRectContainsPoint(), CGRectGetMidX(), CGRectGetMidY(), CGRectIntegral(), and CGRectZero, which all fit under the umbrella of CoreGraphics.  However, the podspec currently doesn't note that it needs CoreGraphics, so if your project doesn't include the framework already, you'll get linker errors (à la http://cl.ly/Rd5S).

This adds it under `s.frameworks` in PonyDebugger's 0.3.0 podspec.
Merge pull request #4302 from capnslipp/master

PonyDebugger uses CoreGraphics