Tests grow the ability to call diff with options. Options to use are encoded in the test file name as a single dash followed by a string of option letters. E.g. -wp for 'ignore whitespace' and 'do patience'

Ensure that a adjacent chunks of same type are combined, and that a minus block always precedes an adjacent plus block. The upcoming myers-divide optimization is prone to produce weird ordering of plus and minus chunks.

In debug output: fix some indents, fix printing of max state size, in myers graph, limit x axis labels to 2 digits, print colored markers of current myers graph positions, also print myers-divide positions in myers graph.