color: use ui.formatted() to test TTYness, not sys.stdout.isatty()
This fixes the color extension not working with pager (broken in
877390020477). The pager extension already sets ui.formatted=True to
allow this use case.
$ hg init
$ echo a > a
$ hg ci -qAm 'add a'
$ echo b > b
$ hg ci -qAm 'add b'
$ hg up -qC 0
$ hg rm a
$ hg ci -m 'rm a'
created new head
$ hg up -qC 1
$ rm a
Local deleted a file, remote removed
Should fail, since there are deleted files:
$ hg merge
abort: outstanding uncommitted changes (use 'hg status' to list changes)
[255]
Should succeed with --force:
$ hg -v merge --force
resolving manifests
removing a
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
(branch merge, don't forget to commit)
Should show 'a' as removed:
$ hg status
R a
$ hg ci -m merge
Should not show 'a':
$ hg manifest
b