sqlalchemy/test/plugin

This is a total hack, as the files here are an exact copy of sqlalchemy/testing/plugin/.

I can't see much solution here as I'd like "noseplugin" to be available to environments
where SQLAlchemy is installed.  However, I also need to be able to load "noseplugin"
*without* importing SQLAlchemy, else coverage doesn't work when testing SQLAlchemy itself.

A solution here would be if there's a way to get coverage to explicitly include
packages that are already imported.  Perhaps like a module reload.

Other solutions that have not worked include:

	* set an extra, fake sys.path for "sqlalchemy/testing/plugins" and import
	  relative to that.  Breaks in Python 3 as the modules in "sqlalchemy/testing"
	  get interpreted as Python builtins (i.e. warnings), and apparently ConfigParser
	  has "import warnings" and it all breaks.

	* Have the noseplugin install as an entirely separate package next to lib/.
	  We did this in 0.6 and users complained, as we also had it enabled as
	  a nose plugin.  just having it there as a "do-nothing", separately installed
	  package, is really awkward.  Doesn't work.



so: TODO

1. fix that pdb you have stuck in _do_skips

2. offload everything in noseplugin that is post-coverage out to
testing/ - mainly _do_skips and the before/after test/context hooks.

3. merge plugins/config into noseplugin.

4. remove test/plugin

5. have sqla_nose.py load noseplugin.py as a single .py file, using
imp or similar.  it has no dependencies outside of sqlalchemy.testing.