Clean session and random client ids

[Roger Light <roger@atchoo.org>]

Hi,

A lot of MQTT client libraries offer the feature of generating random
client ids rather than having to supply one. This is good.

I recently had over 10,000 client connections made to
test.mosquitto.org using a random client id, but also having set clean
session to false, which meant that when they disconnected their
information was stored on the server but there was basically no chance
they could reconnect.

It would be nice to have a comment in the spec suggesting that
implementations may offer to generate random client ids but that they
must refuse to do so if clean session is set to false.

Cheers,

Roger