Fix knife angle constraint bug #33813 by changing knife mvals to floats.

The problem was that by snapping the integer mouse values to
lines through the previous point, the angle was slightly off.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@53730 954f8c5b-7b00-dc11-b283-0030488c597c