add namespace attr to CodeGenerator, can be either MODULE_NAMESPACE or

add namespace attr to CodeGenerator, can be either MODULE_NAMESPACE or
FUNCTION_NAMESPACE.  initialize in __init__ and reset in
generateFunctionCode.

replace direct issue of STORE_FAST, STORE_GLOBAL, etc. with call to
storeName; same for loadName and deleteName

the new {store,load,delete}Name methods use the namespace attr and the
local variable stack to determine the correct bytecode to issue