Add 'cut-through' option for Knife Project operator.

If enabled, it makes knife project act as the
cut-through (Shift-K) version of knife.
This option will soon be more useful when a better
cut-though Knife change is submitted, allowing
this to work for cuts within faces in addition
to cuts across them.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk@61045 954f8c5b-7b00-dc11-b283-0030488c597c