tests/test-diff-issue2761.t

byteify-strings: add support for ignore comments

Our simple token analysis is sometimes not clever enough, we need to be able
to turn off our script for parts of the code.

This change introduces three special comments:

    - `#no-py3-transform` to tell `byteify-strings` ignore the next line
    - `#py3-transform: off` to ignore everything until the end of the file
    - `#py3-transform: on` to stop ignoring

The last two can be particularly useful within Python 2/3 compatibility files.

Test issue2761

  $ hg init

  $ touch to-be-deleted
  $ hg add
  adding to-be-deleted
  $ hg ci -m first
  $ echo a > to-be-deleted
  $ hg ci -m second
  $ rm to-be-deleted
  $ hg diff -r 0

Same issue, different code path

  $ hg up -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ touch does-not-exist-in-1
  $ hg add
  adding does-not-exist-in-1
  $ hg ci -m third
  $ rm does-not-exist-in-1
  $ hg diff -r 1