Set scene frames operator for clip editor.

This operator will set scene's start/end frames to
match clip's start frame and footage duration.

Available in Clip panel in clip editor's toolbox.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56664 954f8c5b-7b00-dc11-b283-0030488c597c