#8 Adding DESTINATIONALLOW request

[Trek Star]

In a remailer scenario where all the remailers are
middleman (due to massive abuse), probably only the
nymservers can send mails to the world (for the enanced
anti-spam tecnology).

In order to support nymservers' reply-blocks, in a
all-remailers-are-middleman-scenario, any remailer
should destination-allow any nym user.

To do this we should create a DESTINATIONALLOW request,
an AUTOALLOW configuration option and make the
DESTINATION* requests like a mailing-list manager (with
encrypted confirmation).