SimObject: add export_method* hooks to export C++ methods to Python

Replace the (broken as of previous changeset) swig_objdecl() method
that allowed/forced you to substitute a whole new C++ struct
definition for SWIG to wrap with a set of export_method* hooks
that let you just declare a set of C++ methods (or other declarations)
that get inserted in the auto-generated struct.

Restore the System get/setMemoryMode methods, and use this mechanism
to specialize SimObject as well, eliminating teh need for sim_object.i.
Needed bits of sim_object.i are moved to the new pyobject.i.
Also sucked a little SimObject specialization into cxx_param_decl()
allowing us to get rid of src/sim/sim_object_params.hh.  Now the
generation and wrapping of the base SimObject param struct is more
in line with how derived objects are handled.

--HG--
rename : src/python/swig/sim_object.i => src/python/swig/pyobject.i

src/python/SConscript

@@ -66,6 +66,7 @@ PySource('m5.util', 'm5/util/terminal.py')
 SwigSource('m5.internal', 'swig/core.i')
 SwigSource('m5.internal', 'swig/debug.i')
 SwigSource('m5.internal', 'swig/event.i')
+SwigSource('m5.internal', 'swig/pyobject.i')
 SwigSource('m5.internal', 'swig/range.i')
 SwigSource('m5.internal', 'swig/stats.i')
 SwigSource('m5.internal', 'swig/trace.i')