context: move contents of committablectx.markcommitted() to workingctx
Same reasoning as previous commits: this function updates the
dirstate. By not updating the dirstate here, we also fix the
close-head test.
Differential Revision: https://phab.mercurial-scm.org/D6365
#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