adding --before first pipe when not on first pipe errors

[Tim Penhey]

$ bzr pipes
   code-review-comment-email-job
   new-reviewer-email-job
* bmp-notification-email-job
   all-code-review-email-using-jobs

$ bzr add-pipe --before move-mailout-functions code-review-comment-email-job
bzr: ERROR: bzrlib.errors.ObjectNotLocked: <bzrlib.groupcompress._GCGraphIndex object at 0x27bc4d0> is not locked

*** Bazaar has encountered an internal error. This probably indicates a
    bug in Bazaar. You can help us fix it by filing a bug report at
        https://bugs.launchpad.net/bzr/+filebug
    attaching the crash file
        /home/tim/.cache/crash/bzr-20100318215534-11484.crash
    and including a description of the problem.

    The crash file is plain text and you can inspect or edit it to remove
    private information.

[Tim Penhey (thumper)]

$ bzr switch :first
Updated to revision 10491.
Switched to branch: /home/tim/repo/canonical/launchpad/code-review-comment-email-job/
$ bzr add-pipe --before move-mailout-functions
Updated to revision 10541.
Created and switched to pipe "move-mailout-functions".

This worked.