mod_rest: Reject password that fails saslprep earlier (thanks tgy) Prevents an error later if/when passing the password through saslprep a second time in the authentication module, since the prep functions now reject nil The error reporting could be improved but that would involve adding a way to pass errors back out of the check_credentials() function.

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.