non-backward compatible changes for some expressions

I'm working on the next version of OpenWFEru, it should be very close to 1.0.

I'm currently cleaning up some process definition language
expressions. Unfortunately the changes I will make to them will render
them incompatible with previous releases' implementation.

These expressions are 'cron' (already talked about it), 'cursor',
'loop', 'iterator' and 'concurrent-iterator', as well as 'listen'.
There will be slight changes for 'when' and 'wait' but they should be
"backward-compatible".

By backward-compatibility, I'm talking about the ability to stop a pre
0.9.18 engine, replace it with a 0.9.18 or later engine and restarting
with processes ready to go.

There will three ways to migrate without [too much] pain :

1). if you don't use any of the mentioned expressions, the move should be safe
2). if you use any of them, making sure that all processes being
migrated are not inside one of those expressions at engine stop time
3). migrate manually (replay manually processes on the new server)
(4). don't migrate)

In the past, I've managed to handle such issues transparently, by
making sure that new implementations handled correctly past
implementations' rundata. But this change behind the scenes is a bit
too big this time.

The goal of these changes is to make process instance visualization
and manipulation easier. These expressions were handled in special
ways and I'm working on making their behaviour and visibility
consistent.

If you have any question, feel free to ask. I'll be glad to clarify
any detail. Best regards,

--
John Mettraux -///- http://jmettraux.openwfe.org