Add a new flag value `CUMA_REMOVE` to explicitly tag duplicate points
for removal. This prevents a bug where all curve points with vector
handles were deleted, when removing duplicate curve points while
updating the widget. This happened, because the flag value used to tag
points for removal was the same as the value of `CUMA_HANDLE_VECTOR`
used to store the handle type of the curve point.
Reviewed By: Hans Goudey
Differential Revision: http://developer.blender.org/D16463
9de35e396b