obslog: add the operation to the Obslog output The operation is helpful when debugging a case where we don't know how we ended up in this case while effect-flag are useful to understand what semantic changes happens to a changeset. Add the operation when displaying an obs-marker in the following form: `rewritten as X using amend` The other proposal is interesting but seems harder to internationalize and might requires update each time we introduce new operation: `Amended as X` Let's use the first proposal right now.

#require test-repo pyflakes

Copied from Mercurial core (60ee2593a270)

  $ cd "`dirname "$TESTDIR"`"

run pyflakes on all tracked files ending in .py or without a file ending
(skipping binary file random-seed)

  $ hg locate 'set:(**.py or grep("^#!.*python")) - removed()' 2>/dev/null \
  > | xargs pyflakes 2>/dev/null