Purdy boundary

[Lars Magne Ingebrigtsen <larsi@ifi.uio.no>]

I think it's important that the multipart boundary be as pretty as
possible.  I'm using


--=-=-=

as the default boundary, and am adding one "=" for each subsequent
(and/or nested) multipart, so we get

--=-=-=
--==-=-=
--===-=-=
--====-=-=

and so on.  (This doesn't work properly in 0.49.)

In 0.50 I've added checks for whether this boundary is unique, and if
it's not, it iterates until it finds a unique boundary.

But is this the prettiest possible boundary?  The two hypens at the
beginning are outside our control, but the rest we can do what we want 
with.  It has to be less than 70 characters long, though.

The concluding boundary has two hypens at the end.  Like this:

--=-=-=--

Hey!  Symmetrical!  Neat!

-- 
(domestic pets only, the antidote for overdose, milk.)
  larsi@ifi.uio.no * Lars Magne Ingebrigtsen