tests/test-xdg.t

index: add a `has_node` method (API)

The new `index.has_node(node)` is to be preferred over:

    `node in index.nodemap`.

This get us closer to be able to remove the `nodemap` attribute of the index.

Differential Revision: https://phab.mercurial-scm.org/D7322

#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 2>/dev/null
  foobar

#endif