Code-completions in console.

Implemented RuntimeAgent.callFunctionOn() which is used by the front-end
to get the list of properties to suggest for completion in console.
squash! code-review fixes

Fixed issues found by Ben, wrapped few more long lines.
squash! objectId string to V8 handle number.
Merge pull request #9 from strongloop/call-function-on

Code-completions in console.