Modified Timezones validation to include linked tz

\DateTimeZone::listIdentifiers() does not return all valid time-zones. My timezone was modified as being a link to another timezone which should keep it working as is (confirmed with current iana TZ Coordinator). But this php function does not return it. Questions and bugs to this where filed and this modifications fixes this issue (Exceptions) that users with up to date tzdata and timezones like America/Montreal, Europe/Nicosia, Asia/Istanbul or Asia/Saigon would have.

(more info at https://answers.launchpad.net/ubuntu/+source/tzdata/+question/239234)
Merge pull request #57 from bksunday/patch-1

Modified Timezones validation to include linked tz