Summary:
Recently I had this scm prompt:
{F64910275}
This is not user friendly. I suggest to output at most one remote bookmark
Also this diff copies `seq.py` from upstream hg repo
Test Plan: Run scm prompt tests on devserver and mac and with '--shell=zsh'
Reviewers: rmcelroy
Reviewed By: rmcelroy
Subscribers: simonfar, wez, mjpieters, #sourcecontrol
Differential Revision: https://phabricator.intern.facebook.com/D4197242
Signature: t1:4197242:1483466446:cd1fe943dc99fde0600a4e20994fa4b0f971f72a
