Better MSGSEP declaration

Recently people have been reporting breakages in various software packages
when the 'From ' line contains a quoted address with spaces.  By
default MHonArc is OK, but the suggested extended MSGSEP declaration
in the documentation will break in this type of situation.

This should work in that type of situation:

   <MSGSEP>
      ^From\s+("[^"]+"@\S+|\S+)\s+\S+\s+\S+\s+\d+\s+\d+:\d+:\d+\s+\d+
   </MSGSEP>

Earl, if you think it's appropriate it might be worth changing in
the documentation.

Chris