-F/--force-rebase has no effect if rebase is disabled by config

--force-rebase has no effect if rebase is disabled through git-config
or git-review config files.

This change ensures -F/--force-rebase "wins" over rebase disabled and
-F/--force-rebase becomes mutually exclusive with -R/--no-rebase.

Change-Id: Idd985a6a7a5b1cffa9bed996bb1ea5907e7d0844
Work toward Python 3.4 support and testing

Change-Id: Ie5b0ac8763a0d137e0aa99b05102d2aa76f60034
Define -T/--no-topic to disable review submit with topic

The option -T/--no-topic disables review with topic (mutually
exclusive with -t/--topic).

It allows to submit:

* a change without your current branch name as topic,
* a change update without updating current topic.

Change-Id: I06309b14246cb455d55c6833ab6adb932995edfa
Align git-review and python -m git_review.cmd behaviors

Currently, python -m git_review.cmd wraps git_review.cmd.main call to
handle correctly unicode in python2 where git-review calls directly
git_review.cmd.main. This change embeds the wrapper inside main in
order to align git-review and python -m git_review.cmd behaviors.

Change-Id: I390e2d68b851299c3b07292b89dee8198068e6aa
Merge "Align git-review and python -m git_review.cmd behaviors"
Merge "-F/--force-rebase has no effect if rebase is disabled by config"
Merge "Define -T/--no-topic to disable review submit with topic"