time: require non-lower letter after Jan/January/Mon/Monday in formats

[rsc]

This is not strictly backwards compatible but I can't imagine anyone depending on the
current behavior.

It is slightly surprising that "Janet" is a time format that becomes
"Febet", "Maret", etc. I wonder if we should require that
Jan/January/Mon/Monday not be followed by a lowercase letter in order to have special
meaning.

[robpike]

Comment 1:

This issue was closed by revision af8426e.

Status changed to Fixed.