zsh completion: update helpers and do not overwrite them

__git_branch_names and __git_command_successful come from Zsh's _git
completion, and might be loaded/available already.
zsh: fix typo with harvest completion: s/__get/__git/)
zsh: call _legit when the autoloading is triggered

Otherwise you have to trigger completion twice on the first invocation.
smart_merge: do not assign `log` in case of GitCommandError

In case of error `why` is used for the `log` argument to `abort`.
It might get changed to also pass on the output from `git merge --abort`
via `log` or something similar though?!
Use `is_published` named arg with `Branch`

This is more explicit when reading the code.
Fix `ImportError: cannot import name Args`

Traceback (most recent call last):
  File "…/usr/bin/legit", line 4, in <module>
    import legit.cli
  File "…/lib/legit/legit/cli.py", line 16, in <module>
    from clint import Args

Ref: https://github.com/kennethreitz/legit/pull/130
Ref: https://github.com/kennethreitz/legit/pull/131
Fixes issue #140 (color at aliases installation)
Change gitpython requirement

The non-numerical parts of version number seems to cause issues with pip. Since the package hasn't been updated on pypi in 3 years, it's probably safe to specify latest version for now.
Fix #140 (color at aliases installation)

Apparently the install command string exceeds the max length of the formatter (in windows at least).
Fix broken stash index by remove date info

Fixed an issue where stash index data would get broken by extra date information.
New 'resync' command
Fix synchronization in git stash
Merge branch 'resync' of https://github.com/bluelaguna/legit into develop
Merge branch 'develop' of https://github.com/TCattd/legit into develop

Conflicts:
	legit/cli.py
Merge branch 'fix-zsh-completion' of https://github.com/blueyed/legit into develop
Merge branch 'unused-var' of https://github.com/blueyed/legit into develop
Merge branch 'use-named-arg' of https://github.com/blueyed/legit into develop
Merge branch 'use-try-except-with-clint-import' of https://github.com/blueyed/legit into develop