Allow keys to be set without expire times. Refs colinmollenhour#33

Prevent cache tag data from being lost in race conditions. Refs colin…

…mollenhour#33

Tracking latest lib/Credis (minor)

Always select db in case connection is used elsewhere.

Merge pull request colinmollenhour#2 from mattheath/master

Update modman URL to point to Github in readme

Fix modman command in README.