Fix outgoing body wrapping in devel, by forwardporting the working code

Fix outgoing body wrapping in devel, by forwardporting the working code
from stable. We were sending out mails unwrapped, so they had really long
lines.
The statement in the comment that many browsers support VIRTUAL is wrong
(has that statement been tested?) because I just tested it in Firefox and
IE6; in both browsers mail bodies were not wrapped at all.

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@7944 7612ce4b-ef26-0410-bec9-ea0150e637f0