run-tests: check if stream is a tty before using color
Previous implementation (e80041832eec) checked only if sys.stderr was a tty
which was less general. Also makes sure that colors is never used if pygments is
not available, irrespective of --color flag value.
Martin von Zweigbergk <martinvonz@google.com> [Fri, 14 Jul 2017 21:44:29 -0700] rev 33560
tests: rewrite test-rebase-detach.t using drawdag
This makes it much clearer because each test case can have exactly the
graph it wants (no extra cruft just because other tests want it).
Differential Revision: https://phab.mercurial-scm.org/D94