Fix vcs interact warnings

[aashish24]

/Users/williams13/work/uvcdath/build_uvcdat/install/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/vcs/Canvas.py:3727: UserWarning: VCS Behaviour changed, in order to interact with window, start the interaction mode with:
x.interact()
warnings.warn("VCS Behaviour changed, in order to interact with window, start the interaction mode with:\n x.interact()")

[doutriaux1]

I will look into figuring out if user is on the prompt and issue the warning only if user is on the prompt