default_week_format variable has gone the way of the Dodo, as have the WEEK() and YEARWEEK() functions. These two functions, along with week_mode (default_week_format) were inconsistent with standards and made redundant by the DATE_FORMAT() function.
Cleaned up the former week_number_from_gregorian_date() function into a simpler, strftime()-based solution in sync with PosgreSQL and SQL/ISO standards.
Clean up of the EXTRACT() function to use new temporal system and produce proper errors on bad temporal values.
NOTE: Test cases for EXTRACT and cleanup of the func_time.test case have not yet been committed.