some changes to scipy_bfgs and scipy_ncg

Some changes have been committed to scipy_bfgs and scipy_ncg. Now they handle more stop criteria, and plotting (via p.plot=1) yields point for every iteration, not just 2 points start-finish joined by direct line.

I intend to implement similar changes for ALGENCAN, but since the solver doesn't have iterfcn ability (ALGENCAN developers had been informed about the issue, but no answer have been obtained), I intend to connect iterfcn to df (gradient) (OO numerical gradient will be used if no user-supplied one will be available).