* en_CA.po: Added a translation for the date format, because the default
	does not show 4-digit years. This avoids the warning at startup, which
	asks the translator to deal with it.
	Note that I used YYYY/MM/DD instead of DD/MM/YYY, because a) It is
  apparrently	the official format for Canada, though the other one is still
  common, and b) date parsing failed with DD/MM/YY in this locale.