deliver_local: quote "From " more liberally

deliver_local: quote "From " more liberally

It seems that when scanning for mails in mbox files, most MUAs just
look for lines beginning with "From ", and not only for "From " lines
after an empty line.  Therefore quote "From " more liberally, and also
implement the mboxro format by quoting />*From / lines that have been
quoted before.

Reported-by: Pierre Frenkiel <pierre.frenkiel@gmail.com>