Suggestion: onPersist function call

I had a need to do some changes on a HopObject before it was
written into storage.  So I made a customized version Helma 1.5.3
to call 'onPersist' function when a HopObject was being written
into the embedded or relational database. 

It would be nice if this was added as a new feature for Helma 1.6.

The way I implemented it was very similar to the 'onInit()' function
by making a copy of the "invokeOnInit" function in Node.java
and changing the names to 'OnPersist' then adding a call to
'invokeOnPersist' in the NodeManager methods 'insertNode' and
'updateNode'.

I will be happy to provide the patches if you like.

Thanks,
Kris