Implement Timespan>>beCanonical from Chronology-Core-cmm.15, accidentally omitted in recent UTC updates.
=============== Diff against Chronology-Core-dtl.38 ===============
Item was added:
+ ----- Method: Timespan>>beCanonical (in category 'squeak protocol') -----
+ "Chronology preserves Timespans that are extracted from DateAndTime's, making Dates, Months and Years in Squeak able to represent a true Timespan of those durations starting at a specific local DateAndTime. In case a canonical version is needed, make the receiver independent of any Timezone by removing it."
+ start makeUTC!