tests/test-push-hook-lock.t

rebase: improve error message on improper phases

The previous error message had two issues: The first issue was that it
wasn't, in fact, an error but a warning, even though it described a
fatal error condition preventing the successful completion of the
command. The second was that it didn't mention the immutable
changesets, leaving the user guessing at the true cause of the error.

The main downside to this change is that we now get an 'abort: can't
abort...' message which technically contradicts itself. In this case,
I blame that on the two uses we have for the word; if it weren't for
backwards compatibility, we could make util.Abort print out 'error:
<whatever>'.

  $ hg init 1

  $ echo '[ui]' >> 1/.hg/hgrc
  $ echo 'timeout = 10' >> 1/.hg/hgrc

  $ echo foo > 1/foo
  $ hg --cwd 1 ci -A -m foo
  adding foo

  $ hg clone 1 2
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg clone 2 3
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ echo '[hooks]' >> 2/.hg/hgrc
  $ echo 'changegroup.push = hg push -qf ../1' >> 2/.hg/hgrc

  $ echo bar >> 3/foo
  $ hg --cwd 3 ci -m bar

  $ hg --cwd 3 push ../2
  pushing to ../2
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files