and fix some bugs.

The basic idea is to track a dependency graph to find executable
messages quickly. This makes the activity system far more efficient,
when you have many inter-dependent messages queued in the tables.

Also, this obsoletes the time shifting in the schedulers,
as executable messages can be found in a more efficient manner.
So the activity parameter "at_date" should work expectedly.

Now the API of validate methods in Activities return a
list of message objects instead of a boolean value. Such
a list contains messages that are depended upon by a given
message.

The validate method in Message accepts a new optional
parameter, check_order_validation, to indicate whether
order validation should be performed. The default behavior
has not changed.

getDependentMessageList is added to ActivityTool, Queue
and Message. This method collects dependent message for
a given message from all activities.

There are some other subtle changes. Look at the diffs for
more details.


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@14039 20353a03-c40f-0410-a6d1-a30d3c3de9de