mod_rest: Handle internal http request errors early and then return Skips over attempted parsing of the payload which usually failed since the body is an error string like "connection refused", so this produced useless errors.

This module blocks configured queries that change server state.

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

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