Bring git up to date with svn r57476.
Merge branch 'master' into cycles-mblur

Merging master branch into cycles-mblur branch. I am doing this because
apparently, I messed up and committed code into master that should have
been in branch. This will fix the change.

The changes I made to the code included adding the UI elements for
selecting the number of steps to export, as well as activate deformation
motion blur for the object.