Small initial steps toward generating C++ param structs

Small initial steps toward generating C++ param structs
from Python object descriptions.  Mostly cleanup of Python
code based on things I encountered trying to figure out
what's going on.  Main reason I'm committing this now is
to transfer work from my laptop to zizzer.

sim/pyconfig/m5config.py:
    Small steps toward param struct generation: all param
    objects should now have a _cppname attribute that holds
    their corresponding C++ type name.

    Made Param ptype attribute an actual type instead of a
    string.  String is still stored in ptype_string.

    Get rid of AddToPath() and Import() (redundant copies
    are in importer, and that seems to be the more logical
    place for them).

    Add a few comments, delete some unused code.
test/genini.py:
    A few fixes to make the environment more compatible
    with what really happens when configs are executed
    from the m5 binary.

--HG--
extra : convert_revision : 9fc8f72cd0c22ba3deada02f37484787342534f2