- Added an add() and subtract() that works on
   sparse and dense vectors.

with floating point types in addition to integer types.

and added overloaded versions of a few image processing functions
to make doing in-place operations slightly more convenient.

to call dot() on two 1x1 matrices which were statically dimensioned.

rather than the node_label type from the min_cut object.  This
should make the interface much less confusing.

works right.

graphs that are regular grids.

ends of the rows.

cuts on an image the result is a displayable binary image rather than
an image which is super dark and hard to view.