Added a try-otherwise-useful encoder algorithm to optimizer.

[alvestrand]

This algorithm will look through the list of other encodings done with the same encoder as the currently best one, and see if there are encoders that give better encodings. - the function WorksBetterOnSomeOtherClip.

The CL also removes the "synthesize cliptime" hack; to remove all results that don't contain cliptime, do this:

grep -L 'cliptime' workdir////.result | xargs rm

The result seems to be a large improvement in number of probes that result in an improvement when running randomly_improve_encoding (current run: 70 improvements to 8 not improved, vs. approx equal numbers before).

[alvestrand]

PTAL

[phoglund]

lgtm