gnus-treat-body-highlight-signature redux

[Lars Magne Ingebrigtsen <larsi@gnus.org>]

And all the other highlighting/washing variables.

Ok; we then have a bunch of variables that say what
highlighting/washing is to be done.  Only text/plain parts should have
this washing applied.  However, some highlighting functions should be
applied to all text/plain parts, while others only to some.  For
instance, the signature highlighting thing should probably only be
applied to the final text/plain part.

So -- we have the following valid values:

nil -- don't do it
t -- always do it
last -- only do it on the last part
N -- a number; only do it on parts smaller than N

These aren't exactly orthogonal values, but perhaps that's not a
problem.

Will This Do?

-- 
(domestic pets only, the antidote for overdose, milk.)
  larsi@gnus.org * Lars Magne Ingebrigtsen