tests/test-check-help.t

commitctx: create the ChangingFiles object directly in the various case

No need to compute all data then create the object, we can create it early and
directly store data in it. We start simple by moving create higher in the
function, but the end goal is to eventually move the creation inside the
`_process_files` function to take advantage of the object there.

#require test-repo

  $ . "$TESTDIR/helpers-testrepo.sh"

  $ cat <<'EOF' > scanhelptopics.py
  > from __future__ import absolute_import, print_function
  > import re
  > import sys
  > if sys.platform == "win32":
  >     import msvcrt
  >     import os
  >     msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)
  > stdout = getattr(sys.stdout, 'buffer', sys.stdout)
  > topics = set()
  > topicre = re.compile(br':hg:`help ([a-z0-9\-.]+)`')
  > for fname in sys.argv:
  >     with open(fname, 'rb') as f:
  >         topics.update(m.group(1) for m in topicre.finditer(f.read()))
  > for s in sorted(topics):
  >     stdout.write(b'%s\n' % s)
  > EOF

  $ cd "$TESTDIR"/..

Check if ":hg:`help TOPIC`" is valid:
(use "xargs -n1 -t" to see which help commands are executed)

  $ testrepohg files 'glob:{hgdemandimport,hgext,mercurial}/**/*.py' \
  > | sed 's|\\|/|g' \
  > | xargs "$PYTHON" "$TESTTMP/scanhelptopics.py" \
  > | xargs -n1 hg help --config extensions.phabricator= > /dev/null