Fixes #1635: CDateFormatter::format() with 'ZZZZZ' pattern used to return timezone in RFC 822 format, now returns in ISO 8601 format as it stated in CLDR.

Fixes #1635: CDateFormatter::format() with 'ZZZZZ' pattern used to return timezone in RFC 822 format, now returns in ISO 8601 format as it stated in CLDR.