Enable options --signoff, --reset-author for pick, reword

Hi,

this is a reroll of the patch series that enables rudimentary support of line options for git-rebase's to-do list commands and reimplements the well-known commands reword and squash in terms of a parameterised do_pick.

I tried to address all the issues raised by Junio in this reroll. Here is a short summary.

- Test that reword behaves like pick regarding the pre-commit hook and executes commit-msg for the new log message.

- Instead of disallowing empty log messages for root commits allow empty log messages for all unchanged commits.

- The patch "root commits are replayed with an unnecessary option" does not change the behaviour of git-rebase but it makes the subsequent patch easier to read.

The hidden agenda is to have one git-commit command line in do_pick that takes care of rewriting commits as they are being replayed, be they parentless or not. The advantage of having one rewrite command instead of one for root commits and one for non-root commits is that changes to the rewrite mechanism entail less code changes. As more rewriting mechanisms are being added to do_pick, it becomes important that they compose well with each other to avoid having a series of amending commits. The -C option conflicts with other ways of substituting the log message, like files and strings, which is why it seems not to compose so well.

- The patch "explicitly distinguish replay commands and exec tasks" does not change behaviour either but is again a separated refactoring patch.

The distinction of the exec command and the replay commands, which all share the same line format command args sha1 rest, allows us to employ the positional parameters feature of the shell without introducing another indentation level in do_pick.

Thanks for your time,
Fabian

Fabian Ruch (19):
rebase -i: failed reword prints redundant error message rebase -i: allow rewording an empty commit without complaints rebase -i: reword executes pre-commit hook on interim commit rebase -i: teach do_pick the option --edit
rebase -i: implement reword in terms of do_pick
rebase -i: allow replaying commits with empty log messages rebase -i: log the replay of root commits
rebase -i: root commits are replayed with an unnecessary option rebase -i: commit only once when rewriting picks
rebase -i: do not die in do_pick
rebase -i: teach do_pick the option --amend
rebase -i: teach do_pick the option --file
rebase -i: prepare for squash in terms of do_pick --amend rebase -i: implement squash in terms of do_pick
rebase -i: explicitly distinguish replay commands and exec tasks rebase -i: parse to-do list command line options
rebase -i: teach do_pick the option --reset-author
rebase -i: teach do_pick the option --signoff
rebase -i: enable options --signoff, --reset-author for pick, reword

 git-rebase--interactive.sh    | 284 ++++++++++++++++++++++++++++++++++--------
 t/t3404-rebase-interactive.sh |  70 +++++++++++
 t/t3412-rebase-root.sh        |  19 +++
 t/test-lib-functions.sh       |   6 +-
 4 files changed, 325 insertions(+), 54 deletions(-)

2.0.1