Code review comment for lp:~gz/testtools/unprintable-assertThat-804127

Okay, this branch should now be tidied up enough to land, can you see anything I've missed?

I tried out switching the repr-like function to take any object, and it does seem to be a better interface but complicates the logic even further, so should probably be done separately.

There's still a bunch of todo all over the place, and I haven't managed to squish _isbytes yet, though it's not strictly necessary in the matchers code bar some new tests I added that expect fancy behaviour.

There are a couple more interesting things that could do with handling later. Either Annotate or AnnotateMismatch (or both, see the earlier complaint about string typing) should check the message they are given is printable unicode. Also the regular expression display form could do with some extra testing, I'm not totally convinced it always produces correct expressions (and certainly doesn't with some on Python 2.4 where the unicode-escape codec fails to escape backslashes).