NAME
----
ping

DESCRIPTION
-----------
Requests an "echo" for test purposes.

ARGUMENTS
---------
any

RESPONSE
--------
Message of type 'echo' containing the arguments of the 
'ping' message (see below).

NOTES
-----
The 'ping' message type may be used for testing the
server, the client and the communication channel between
them, as well as or for retrieving the server's public key. 
Any arguments are accepted and will be returned unchanged
in the 'echo' message.

If the 'ping' message is signed, the server will try to
verify the signature using the sender ID ('From' field) or 
the public key provided in the message ('Public-Key' field).
The result of the verification will be included in the
'Verification-Result' field of the echo.

If the 'ping' message contains an encrypted field named xyz~,
the echo will contain a field Decrypt-xyz with the
decrypted value.

If the 'ping' message contains a field named Encrypt-xyz,
the echo will contain a field xyz~ with the original
value encrypted.