tests/test-dirstate-backup.t

hgweb: perform all parameter lookup via qsparams

I think I managed to update all call sites using wsgirequest.form
to use parsedrequest.qsparams.

Since behavior of qsparams is to retrieve last value, behavior will
change if a parameter was specified multiple times. But I think this
is acceptable.

I'm not a fan of the `req.req.qsparams` pattern. And some of the
modified code could be written better. But I was aiming for a
straight port with this change. Cleanup can come later.

Differential Revision: https://phab.mercurial-scm.org/D2781

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