* rulesets/PythonWrapper.cpp: Make sure PythonWrapper holds a propper
reference to the wrapper object, to ensure its not dealloced.
* rulesets/Py_Location.cpp: Store a PythonWrapper when creating
a new wrapper object if the entity does not already have
a script.
* rulesets/MemMap.cpp: Fix an uninitialised variable.
* rulesets/PythonWrapper.h, rulesets/PythonWrapper.cpp: Add new
class which inherits from Script to store a wrapper pointer
for instances which have no script.
* rulesets/PythonScript.h, rulesets/PythonScript.cpp,
rulesets/PythonThingScript.h, rulesets/PythonThingScript.cpp,
rulesets/PythonMindScript.h, rulesets/PythonMindScript.cpp:
Refactor script classes to inherit from PythonWrapper to make
storing wrappers for mind and world entities easier.
* rulesets/Py_Location.cpp, rulesets/Py_World.cpp: Use PythonWrapper
interface to get wrapper pointers from Script objects.
* rulesets/Python_API.cpp: Improve variable names, and comment out
some unused code.
