Fix MAGN-5365  Crash with either Point.Origin or Vector.ZAxis wired to Watch node 

This pull request fixes defect [MAGN-5365  Crash with either Point.Origin or Vector.ZAxis wired to Watch node](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-5365).

That is because csharp marshler doesn't support unmarshl function pointer. Here we simply bind it to itself and return the value in ``StackValue`` format, watch node internally will handle ``StackValue`` typed input. 

To display more meaningful value in watch node, I extended ``StringUtils.GetStringValue()`` for function pointer, so it will return qualified function name in string format. Example:

![untitled](https://cloud.githubusercontent.com/assets/2600379/4988074/126b9ab4-6998-11e4-982b-860ddcb2487c.png)

Regression test case ``WatchNodeTest.watchFuncitonPointer`` is added.

@sharadkjaiswal, @Steell  please review the change
@riteshchandawar please review new test case.