Only allow SimObject classes to be instantiated (no cloning!).

Only allow SimObject classes to be instantiated (no cloning!).
Provide a makeClass() method to generate a new class using
a SimObject instance as a template.
All instantiation, subclassing, and class generation is done
recursively using "deep copy"-style memoization to maintain
object relationships in the face of multiple references to
shared objects/classes.

src/python/m5/multidict.py:
    Rename local dict attribute from 'dict' to 'local'
    for clarity.

--HG--
extra : convert_revision : 73ed6836216308709d7bb68d09f8131acd5f1822