This takes the advice from
http://files.stairways.com/other/ftp-list-specs-info.txt
further: search for the date by an explicit occurrence of a known month
name. This means that we won't see files with bad names (they'd be
filtered out of the result), but the filtered out entries are ones that
would not be usable with `ftp-make-file-seconds'.
When the month is found, and the entry is a file, look for a number
preceding the month, and if found, return it as the file size string.
This is a minor change in the API. (But it's probably better to either
revise it further, or eventually make it irrelevant by exposing the
interesting functionality via `net/url'.)
6a1336e75e