Change options of pdb plugin

Support --pdb-errors, --pdb-failures, and --pdb (both)

This fixes #366.
Change links on docs sidebar

* Remved "Older Versions" section that contained broken links
* Fixed link to pytest
* Fixed "Current Version" link to pypi to link to current version
* Removed link to old and unused announcement mailing list

This fixes #374
Catch KeyboardInterrupt during test run...

...so that one can ^C a test run and still get a report of failed tests
and stack traces.
xunit: don't claim to take multiple args in Tee.write()
Fix #680: xunit problem with unicode on stdout

It turns out we were trying to write unicode strings into a
cStringIO.StringIO object, which doesn't work well with unicode strings.
Instead, lets use StringIO.StringIO objects for capturing stdout and
stderr.
Added NOSE_IGNORE_CONFIG_FILES as env variable option
Fix #649: UnicodeDecodeError when an exception contains encoded strings

The issue stems from the fact that when you use a coding line in the
Python file, and raise an exception that contains unicode characters,
the message in the exception is an encoded string.  We need to get it
converted into unicode, but simply calling `unicode(ev)` doesn't work,
as that often fails with a `UnicodeDecodeError` because it assumes
`ascii` encoding by default.

This fixes the issue by trying to decode the stream as UTF-8, and uses
replacement on errors.  It's not ideal, but the best we can do since
we don't know the encoding of the message string.

Thanks to Christoph Zwerschke for the test case.
Fix #687: verbosity is not a flag

The issue is that `nosetests.cfgToArg()` was treating the verbosity flag
as a boolean when you set the value to `1` in `setup.cfg`.  Instead of
using the `flag()` helper, let's consult the option object and see if
the action is `store_true` or `store_false`.
Merge pull request #666 from Infinidat/366

Make `--pdb` launch pdb for both errors and failures, and introduce a `--pdb-errors` to get the previous behavior.
Merge pull request #679 from Infinidat/374

Fix #374: "Older Versions" link broken on home page, and a few other issues.
fix suppressed deprecation warning

Python's default warning filter suppresses deprecation warnings;
Change the filter to make the warnings in nose.config visible.
Merge pull request #668 from Infinidat/388

Fix suppressed deprecation warning.
Merge pull request #688 from jszakmeister/fix-issue-687

Fix #687: verbosity is not a flag
Merge pull request #686 from jszakmeister/fix-issue-649

Fix #649: UnicodeDecodeError when an exception contains encoded strings
Merge pull request #684 from jszakmeister/fix-xunit-unicode

Fix xunit when writing unicode to stdout and stderr.
Removed doubled word
Look for unittest2 in skip plugin

If unittest2 is available, try to use its SkipTest class rather than a
nose internal version.  Inspired by better integration with testtools
for older python releases (see [1]).

[1] https://review.openstack.org/#/c/33056/
Fix #700: Tee is missing the writelines() method.
Add a fake isatty() method to Tee.
Failing test for modules with names starting with __init__ that aren't __init__.py