tests/test-backwards-remove.t

tests: pull common http server setup out of individual tests

There are currently two different tests using roughly the same code to
create temporary scripts acting as HTTP servers. As there is going to
be at least one more in an upcoming change, factor those out in a
standalone dumbhttp.py script.

  $ hg init
  $ echo This is file a1 > a
  $ hg add a
  $ hg commit -m "commit #0"
  $ ls
  a
  $ echo This is file b1 > b
  $ hg add b
  $ hg commit -m "commit #1"
  $ hg co 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

B should disappear

  $ ls
  a