BETWEEN was more lenient with regard to what it accepted as a DATE/DATETIME
in comparisons than greater-than and less-than were. ChangeSet makes < >
comparisons similarly robust with regard to trailing garbage (" GMT-1")
and "missing" leading zeros. Now all three comparators behave similarly
in that they throw a warning for "junk" at the end of the data, but then
proceed anyway if possible. Before < > fell back on a string- (rather than
date-) comparison when a warning-condition was raised in the string-to-date
conversion. Now the fallback only happens on actual errors, while warning-
conditions still result in a warning being to delivered to the client.


mysql-test/r/select.result:
  Show that we compare DATE/DATETIME-like strings as date(time)s
  now, rather than as bin-strings.
  Adjust older result as "2005-09-3a" is now correctly seen as
  "2005-09-3" + trailing garbage, rather than as "2005-09-30".
mysql-test/t/select.test:
  Show that we compare DATE/DATETIME-like strings as date(time)s
  now, rather than as bin-strings.
sql-common/my_time.c:
  correct/clarify date-related comments, particulary for check_date().
  doxygenize comment while at it.
sql/item_cmpfunc.cc:
  get_date_from_str() no longer signals an error when all we had
  was a warning-condition -- and one we already gave the user a
  warning for at that. Preamble doxygenized.