Improve Resque_Redis DSN parsing.

- Allow for DSN URIs to work as expected.
- Backward-compatible with simple 'host:port' format.
- Does not parse DSNs provided in array format for Credis_Cluster.
Improve comments and readability
Test for 'false' database value when not found in DSN
Put 'else' keyword on new line in keeping with project conventions
Make parseDsn() method static, remove unused member vars
Add comment describing REDIS_BACKEND format to bin/resque
Fix return array format of `bogusDsnStringProvider`
Revert file modes back to 644
Merge pull request #186 from iskandar/dsn-normalization

DSN and REDIS_BACKEND normalization