tests/test-gendoc-zh_TW.t

phase: handle phase with no command flag

Before this changeset, all existing phases have a corresponding flag on the `hg
phase` command. (eg: `hg phase --draft`).

After this changeset, a phase can exists without having an associated flag.
This is useful to introduce a new internal phase that we do not want to expose
to user.

#require docutils gettext

  $ $TESTDIR/check-gendoc zh_TW
  checking for parse errors