Storm's DEBUG mode should include the database URI when outputting queries

[Jamu Kakar]

Today while debugging a problem it seemed that two identical queries
were being run. Eventually it was determined that they were running
against different databases. It would be nice if the output generated
when storm.database.DEBUG is True included the URI of the database the
query is being run against.

[Jamu Kakar (jkakar)]

The branch attached to this bug is ready for review. It introduces
the following changes:

- Store and Database objects have a uri property that exposes the URI
  object they use.

- URI objects represent themselves in the standard textual format when
  stringified.

- The URI is included in statement output when storm.database.DEBUG is
  True.

[Gustavo Niemeyer (niemeyer)]

Nice idea! I'd like to use these ideas on execution tracing that I'm working on.
OTOH, there are a few issues with this branch, so rather than trying to integrate
it on trunk, I'll just move it forward.

Specific issues I've noticed:

[1]

The port parameter handling in URI.__str__ is untested, and will break the
method if passed, because it's an integer.

[2]

There's no escaping handling in URI.__str__.

[3]

If only the password is passed in, the uri produced is broken because '@' isn't
added between the password and the hostname.

[4]

If the host part isn't provided, the uri is broken because '@' isn't added after the
username and/or password.

[5]

I think we should expose store.database instead of store.database.uri as store.uri
directly.

[6]

Rather than having all database backends setting self.uri = uri, we should have a
common constructor in Database.__init__ which does it.

[Jamu Kakar (jkakar)]

Gustavo's taking the useful bits from here and integrating them in his
tracing branch.