ui: add 'force' parameter to traceback() to override the current print setting
This will allow a current traceback.print_exc() call in dispatch to be replaced
with ui.traceback() even if --traceback was not given on the command line.
$ "$TESTDIR/hghave" execbit || exit 80
$ hg init repo
$ cd repo
$ echo foo > foo
$ chmod 644 foo
$ hg ci -qAm '644'
$ chmod 755 foo
$ hg ci -qAm '755'
reverting to rev 0
$ hg revert -a -r 0
reverting foo
$ hg st
M foo
$ hg diff --git
diff --git a/foo b/foo
old mode 100755
new mode 100644
$ cd ..