py3: add some r'' prefixes in hgext/narrow/narrowwirepeer.py
This fixes test-narrow-widen-no-ellipsis.t on Python 3.
# skip-blame because just r'' prefixes
Differential Revision: https://phab.mercurial-scm.org/D5023
#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