tests/test-xdg.t

templater: port formatnode filter from changeset_templater

This slightly reduces the difference between changeset_templater and formatter,
and helps extending formatter to support changeset templating.

New formatnode() is not a template filter, but a function since a filter
cannot access to ui. And it's marked as DEPRECATED since I think it exists
only for compatibility reasons.

#if no-windows no-osx

  $ mkdir -p xdgconf/hg
  $ echo '[ui]' > xdgconf/hg/hgrc
  $ echo 'username = foobar' >> xdgconf/hg/hgrc
  $ XDG_CONFIG_HOME="`pwd`/xdgconf" ; export XDG_CONFIG_HOME
  $ unset HGRCPATH
  $ hg config ui.username
  foobar

#endif