The date format `%Y%m%d%H%M` will successfully match against
one-digit month, day, hour, and minute strings, even though %m et al.
are documented as being zero-padded. So dates without time in
Nov/Dec may be wrongly parsed as dates in January with time.
This commit adds a format string of `%Y%m%d` to our supported date
format strings directly below (higher priority) its problematic relatives.
Closes#2076
Authored by: wlritchi
4f3fa23e5a