About asynchronous message handlers
Edmund Edgar, 2012-04-20

The message_handlers directory is for files that handle messages that are put in a message queue.
This will only be used if your installation has some kind of queue mechanism. 

These are called by sloodled.php, which is intended to be run as a background process.
There may be many instances of sloodled.php running at the same time.

As of 2012-04-14 we are using the Beanstalk daemon which has to be turned on in sl_config.
On ubuntu you install this with apt-get install beanstalkd.
In future we'll probably make an SQL table to do this without the need to run beanstalkd, albeit less efficiently.
We will also make a method to poll the message queue from in-world and relay the results to the addresses that need them.
This will also make sloodle 2 usable by people who can't get http-in messages through from their Moodle because of firewall issues.

The message handlers take the form:
 <taskname>_request.php
 <taskname>_response.php

eg. for the task "derez",
 derez_request.php
 ...handles making a request to derez an object, which involves sending a message to the object, while
 derez_response.php
 ...handles the answer to that request, which involves deleting the object's active_object entry.

The response handlers are optional - if you don't make one, the result will be ignored.

The job will be deleted once the handler completes, regardless of the result.
If you want to temporarily abandon the task and retry it, exit.

