v2, 2 partsbisect--helper: string output variables together with "&&"

The goal of this 2 patches is to get rid of the need to pipe the output of "eval 'git bisect--helper --next-vars'" into a "while read" loop.

The only change since the previous version is that a brown paper bag bug in "show_tried_revs" is fixed in the second patch.

  rev-list: pass a flag as last argument of "show_bisect_vars"
  bisect--helper: string output variables together with "&&"

 bisect.c           |    3 ++-
 bisect.h           |    9 +++++++--
 builtin-rev-list.c |   42 +++++++++++++++++++++++++-----------------
 git-bisect.sh      |   15 +--------------
 4 files changed, 35 insertions(+), 34 deletions(-)