tests/test-dirstate-backup.t

manifest: change terminology for storage in context classes

Storage may not be backed by revlogs. So it is wrong to refer
to storage as "revlog" or use abbreviations like "rl."

This commit replaces revlog terminology in manifest context classes
and starts referring to things as "store" or "storage."

Differential Revision: https://phab.mercurial-scm.org/D4389

Set up

  $ hg init repo
  $ cd repo

Try to import an empty patch

  $ hg import --no-commit - <<EOF
  > EOF
  applying patch from stdin
  abort: stdin: no diffs found
  [255]

No dirstate backups are left behind

  $ ls .hg/dirstate* | sort
  .hg/dirstate