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.

No reason to expose a daemon to all interfaces when it is only used for
tests, which connect to localhost anyway.
I'd love to use localhost here instead, but the git-daemon man page points out:

    If IPv6 is not supported, then --listen=hostname is also not
    supported and --listen must be given an IPv4 address.

I don't know of a way to check if git has ipv6 support, but 127.0.0.1
should be around for the foreseeable future

When pushing/pulling, we ignore errors unless it's exit code 128.
The reason for this is now made explicit to make clear that issues
are handled by PushInfo flags accordingly.

Related #271

Latest version of it is required to show the issues travis shows as well

That way they are protected from regression.

Fixes #239

This will save IOPs, and make the code easier to understand (I suppose).

Related to #224

That way, we don't try to compare a real-path to a non-real one, which would make the implementation think
a file is not actually part of the repository.

Fixes #224

At least leakage is considerably reduced.
Additionally, a test-case was added which triggers failure if auto-disposal
of resources wouldn't work.

Fixes #60