pool: handle server connection state

Add server state tracking to the pool connection. The connection Close
method clears watch and transaction state. If a subscription or monitor
command was used, the underlying connection is closed.

Fixes issue #53.
Update doc to new and improved Redis terminolgy
Improve pool documentation.
Improve pool documentation.
Fix typo in docs
Merge pull request #58 from wricardo/master

Fix typo in docs
Cleanup pub/sub state on pool close.
Rename DialTest to DialTestDB.

Also, add doc comments to the dial() and DialTestDB() functions.
Fix doc typo
Merge pull request #61 from kjk/patch-1

Fix doc typo
Remove line left from debugging session.
Merge pull request #1 from garyburd/master

Update redigo with author's commits