Fixes issues with Date object and tz-specific tests

- Date tests weren't passing outside of EDT/EST. Now passes in all
  timezones tested.
- Extends Date parsing to account for timezones with 2-5 letter
  abbreviations.
- Fixes bug with Date#getYear: UTC vs. local year
- Additional tests for tz-specific behavior in other timezones (using
  conditional assertions).
Merge branch 'master' of github.com:ndreynolds/flathead