chg: use color in debug/error messages conditionally Before this patch, chg always uses color in its debugmsg and abortmsg and there is no way to turn it off. This patch adds a global flag to control whether chg should use color or not and only enables it when stderr is a tty and HGPLAIN is not set.

revset: force ascending order for baseset initialized from a set It is possible to initialize a baseset directly from a set object. However, in this case the iteration order was inherited from the set. Set have undefined iteration order (especially cpython and pypy will have different one) so we should not rely on it anywhere. Therefor we declare the baseset "ascending" to enforce a consistent iteration order. The sorting is done lazily by the baseset class and should have no performance impact when it does not matter. This makes test-revset.t pass with pypy.