Fixed broken spec.

ActiveSupport added 2 new timezones which broke the current specs.
Added ability to force a unique list of timezones based on the tzinfo.indentifier attribute.

Basically, this prevents multiple time zone values from appearing as select options. Example: "Pacific/Midway" would only appear once.
Cleaned up code which creates the unique zones.
Merge pull request #3 from jrmyward/feature/force-unique-time-zone-values

Feature/force unique time zone values