[Chandler-dev] added support for Decimal values

[Andi Vajda]

In Python 2.4, the decimal module was added.
The repository now supports persisting values of type decimal.Decimal.

I added a new //Schema/Core/Decimal type item for this purpose and Morgen made 
the corresponding change to the schema API.

For more information on this new python type, please refer to:
     http://www.python.org/doc/current/lib/module-decimal.html

Andi..