mod_sasl2_bind2, mod_sasl2_sm: Remove bind2 <features/> wrapper element
This was dropped from the spec. It's more consistent with SASL2.
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.