[PATCH 0 of 1] color: diff colorization (revised with Georg Brandl's patch)

[Brodie Rao]

Here's a new version of my diff colorization patch. I've incorporated Georg
Brandl's patch into my own, which wraps changeset_printer.showpatch() for
log, outgoing, etc., so colorization doesn't interfere with non-patch output.

This patch explicitly wraps log, outgoing, etc. to wrap changeset_printer, so
--no-color/--color work with those commands. The terminal detection code has
been revised with advice from Brendan Cully (isatty check moved into a
function so it can be short circuited).

The patch is against crew. It depends on recent fixes to color by Brendan.