Merge branch 'no-empty-commits'

Avoid creating empty commits if the user opens the instruction sheet and
then decides to close it again without making any changes.

* no-empty-commits:
  Don't create empty commits in the instruction ref
Merge branch 'walk-commits-in-status' into pu

* branch walk-commits-in-status:
  status: include SHA-1 of merge to integration branch
  t3002: add a test with multiple up-to-date branches
  status: Extract status_base as a separate step

Show the SHA-1 of the merge which brings a branch into the integration
branch in the --status output.

I'm not completely convinced that this is a good thing...
Merge branch 'fixup-instruction' into pu

* branch fixup-instruction:
  Add a "fixup" instruction

The basic functionality is simple and working, but the --status output
is more interesting and I'm not convinced the current heuristic is
sufficiently robust.  The implementation in status_fixup could also
use some refactoring.
Merge branch 'skip-option' into pu

* branch skip-option:
  WIP
  Add --skip option

Needs more work to be able to handle "branch not found".