infinite weights on some edges.

to static_casts whenever it was possilbe to do so.

The manpages seemed to indicate that the previous code was
correct so I'm not sure if this was a bug or not.  It's been
in dlib for years without causing trouble though.

 - 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.