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 logs events where more than a certain amount of CPU time was
spent.

``` lua
log_cpu_threshold = 0.01 -- in seconds, so this is 10 milliseconds
```

Uses the Lua
[`os.clock()`](http://www.lua.org/manual/5.2/manual.html#pdf-os.clock)
function to estimate CPU usage.