mod_firewall: Initialize compiled chunk just once for all handlers This should fix a case where some stateful dependencies (such as throttles) produce separate instances for every call to new_handler(), leading to surprising behaviour (e.g. rules executed via JUMP CHAIN vs ::deliver would have separate rate limits). This also adds better error handling in case the compiled code fails to run for some reason.

# Introduction

This module sends a [version query][xep0092] to clients when they
connect, and logs the response, allowing statistics of client usage to
be recorded.

Note that since this is per connection, there will be a bias towards
mobile clients on bad connections.

## Example

    info    Running Running Swift version 4.0