tests: add test where copy source is deleted and added back
This shows another difference between pathcopies() and mergecopies():
mergecopies() considers files that have been deleted and then added
back as different files, but pathcopies() does not.
Differential Revision: https://phab.mercurial-scm.org/D6330
#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