Both commands enable handling of a little known feature
of git, which is to support multiple URL for one remote.
You can add multiple url using the `set_url` subcommand of
`git remote`. As listing them is also handy, there's a
nice method to do it, using `get_url`.

* adding set_url method that maps to the git remote set-url command¶
 * can be used to set an URL, or replace an URL with optional positional arg¶
 * can be used to add, delete URL with kwargs (matching set-url options)¶
* adding add_url, delete_url methods that wraps around set_url for conveniency¶
* adding urls property that yields an iterator over the setup urls for a remote¶
* adding a test suite that checks all use case scenarii of this added API.¶

Signed-off-by: Guyzmo <guyzmo+github@m0g.net>

Don't allow `, ` prefixes or suffixes in messages.

Fixes #438

It turns out we can't deal do fetches if no refspec is set as git
will change the format of the fetch return values, providing less
information than usual.

A test was added to show that such a case will fail, and an assertion
will assure we don't attempt to fetch/pull if there is no refspec
for 'fetch'.

Closes #296

add a GIT_PYTHON_TEST_GIT_DAEMON_PORT to set a port other than 9418,
for example for when you already have a daemon running on that port.

Do not swallow non-zero exit status during push and fetch unless
we managed to parse head information.

This behaviour will effetively handle cases were no work was done
due to invalid refspecs or insufficient permissions.

Fixes #271

While at it, all other invocations of .git in remote.py were reviewed

Fixes #262

They are just skipped.

Fixes #249

Need latest master to proceed with test
Conflicts:
	doc/source/tutorial.rst

Even though the test-csae only verifies this spec:
	+refs/pull/*:refs/heads/pull/*
I could locally verify that it indeed handles other ones just as well:
	+refs/pull/*:refs/pull/*

Fixes #243