tests/test-issue842.t

tests: run check-code with warnings and maintain a whitelist

check-code has fine warning checks, but they are a bit noisy and nobody used
them.

Now the warnings will be run in the test suite, where a list of accepted
warnings will be maintained.

Those who introduce or touch a line with a warning will now have to update the
whitelist ... or fix the warning.

http://mercurial.selenic.com/bts/issue842

  $ hg init
  $ echo foo > a
  $ hg ci -Ama
  adding a

  $ hg up -r0000
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ echo bar > a

Should issue new head warning:

  $ hg ci -Amb
  adding a
  created new head

  $ hg up -r0000
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ echo stuffy > a

Should not issue new head warning:

  $ hg ci -q -Amc

  $ hg up -r0000
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ echo crap > a
  $ hg branch testing
  marked working directory as branch testing

Should not issue warning:

  $ hg ci -q -Amd