+ Mark all unused vars and other non-pep8  (PyDev) warnings
+ test_utils:
  + enable & fix forgotten IterableList looped path.
  + unittestize all assertions.
+ remote: minor fix progress dispatching unknown err-lines

Assure that gpgsig is not initialized with None
to allow the automatic deserialization to kick in.

Fixes #500

Previously, GitPython chokes on this while decoding.  Rather than
choking, instead accept the error and replace the invalid bytes by the
� (\x80) char.

This adds 2 properties to commits.  Their values are derived from the
existing data stored on them, but this makes them more conveniently
queryable:

    - authored_datetime
    - committed_datetime

These return "aware" datetimes, so they are effectively companions to
their raw timestamp equivalents, respectively `authored_date` and
`committed_date`.

These datetime instances are convenient structures since they show the
author-local commit date and their UTC offset.

Related to #362

When the code is run without setting up loggers, the loggers have no
handlers for the emitted messages. The logging module displays:
`No handlers could be found for logger "git.cmd"` on the
console. By adding a NullHandler (a no-op) the message disappears,
and doesn't affect logging when other handlers are configured.

In repositories like

	> git branch -a
	* test
	> ls
	test

`repo.iter_commits` failed due to an ambigous argument
(`'git rev-list test`).
Now this cannot happen anymore.

fixes #264