POP3 Spec and mail drop/ Mail store organization

These are more or less nits but some of them are a fairly large
ones (and the IMAP spec should be checked to be sure it doesn't
suffer from any of the same problems).

The second paragraph of Section 3.1 starts "Maildrops can
natively store UTF-8 or be limited to ASCII.".  Essentially the
same statement appears at the beginning of paragraph 4 only it
says "mail store" rather than "maildrop".

Issues:

(1) I'm not quite sure what the difference is between a
"maildrop" and a "mail store".  If there isn't one, the
terminology should be harmonized.  FWIW, RFC 1939 mentions
"maildrop" in several places but never mentions a "mail store"
(or "mailstore").  If there is a difference, the document should
probably go to a little more effort to identify it.  

(2) The second paragraph of Section 3.1 starts "Maildrops can
natively store UTF-8 or be limited to ASCII."  As the inclusive
statement that appears to be, it is flat wrong.  First, if the
maildrop uses Unicode, we don't care what is stored "natively",
with various flavors of UTF-16 or UTF-32 being likely (and
common).  We don't even care if messages are stored in whatever
Charset arrives over the wire (and, indeed, storage of messages
in the form in which they were delivered may be common).  We
require that headers be either ASCII or UTF-8 on the wire, but
that says almost nothing about either maildrop storage form or
message content.  What we care about is that, if the messages
are delivered across a POP3 interfaces with UTF-8 enabled, the