status: do not depend on rebase reflog messages

status: do not depend on rebase reflog messages

b397ea4 (status: show more info than "currently not on any branch",
2013-03-13) attempted to make the output of 'git status' richer in
the case of a detached HEAD.  Before this patch, with a detached
HEAD, we saw:

  $ git status
  # Not currently on any branch.

But after the patch, we see:

  $ git checkout v1.8.2
  $ git status
  # HEAD detached at v1.8.2.

It works by digging the reflog for the most recent message of the
form "checkout: moving from xxxx to yyyy".  It then asserts that
HEAD and "yyyy" are the same, and displays this message.  When they
aren't equal, it displays:

  $ git status
  # HEAD detached from fe11db.

so that the user can see where the HEAD was first detached.

In case of a rebase [-i] operation in progress, this message depends
on the implementation of rebase writing "checkout: " messages to the
reflog, but that is an implementation detail of "rebase".  To remove
this dependency so that rebase can be updated to write better reflog
messages, replace this "HEAD detached from" message with:

  # rebase in progress; onto $ONTO

Changes to the commit object name in the expected output for some of
the tests shows that what the test expected "status" to show during
"rebase -i" was not consistent with the output during a vanilla
"rebase", which showed on top of what commit the series is being
replayed.  Now we consistently expect something meaningful to the
end user.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>