mod_sasl2_fast: Fixes to make channel binding work again tls-endpoint isn't a thing that exists. Also, we needed to copy more channel binding state from the primary sasl_handler. Ideally we'd have a cleaner way to do this, but I think that's part of more substantial changes that the SASL API deserves.

This module blocks configured queries that change server state.

E.g. to make vCard storage read-only:

``` lua
readonly_stores = {
	vcard = { "vcard-temp", "vCard" };
}
```