Addresses this Ubuntu bug:
https://bugs.launchpad.net/ubuntu/+source/matplotlib/+bug/278764 Display a warning when show() is called with a non-GUI backend, so that the user is not left scratching their head when running "ipython -pylab"
Authored by: mdboom 2008-10-08
Parent: [r6167]
Child: [r6169]
