Documentation fixes.

doc/customizing.txt, doc/design.txt
    Documented 'db.curuserid'.
doc/design.txt
    Reflowed to 72 columns (even the layer cake fits :)
roundup/mailgw.py
    Strip '\n' introduced by rfc822.readheaders

Author: Jean Jordaan

doc/customizing.txt

@@ -2,7 +2,7 @@
 Customising Roundup
 ===================
 
-:Version: $Revision: 1.91 $
+:Version: $Revision: 1.92 $
 
 .. This document borrows from the ZopeBook section on ZPT. The original is at:
    http://www.zope.org/Documentation/Books/ZopeBook/current/ZPT.stx
@@ -1622,6 +1622,10 @@ you want access to the "user" class, for example, you would use::
   db/user
   python:db.user
 
+Also, the current id of the current user is available as
+``db.curuserid``. This isn't so useful in templates (where you have
+``request/user``), but it can be useful in detectors or interfaces.
+
 The access results in a `hyperdb class wrapper`_.