Add the "backup files" types to .gitignore

*~ and *.bak
Change an assert() to a Q_ASSERT() in qAppWelcomeScreen

It caused the build to crash on Ubuntu 14.04
Fix issue #46: Disable the build of CompareVolumes

CompareVolumes is a Remote Module of Slicer.
Merge pull request #50 from matthieuheitz/DeleteCompareVolumesModule

Fix #46: Delete CompareVolumes module
Bump Slicer to include fix for the editor

Fixes issue #52