Merge branch 'os/bisect-runs-show-branch-without-pager' into jch

When "git bisect" spawns "git show-branch" to pretty-print the
title of the commit to be tested, it could have invoked user's
pager if user configured to run pager while running show-branch.
The invocation of show-branch has been changed to disable pager,
even if one is configured.

* os/bisect-runs-show-branch-without-pager:
  bisect: disable pager while invoking show-branch