BUG: Ensure application can be killed using CTRL-C. Fixes #3804

This commits fixes a regression introduced by the addition of the
SlicerExtensionWizard module. See inlined comment for more details.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23567 3bd1e089-480b-0410-8dfb-8563597acbee