python string conversion

- use _PyUnicode_AsStringAndSize where possible
- use %R for PyErr_Format(...) rather then running repr on the object explicitly 
- use const char

source/blender/python/generic/IDProp.h

@@ -61,7 +61,7 @@ int BPy_Wrap_SetMapItem(struct IDProperty *prop, PyObject *key, PyObject *val);
 
 
 PyObject *BPy_IDGroup_WrapData(struct ID *id, struct IDProperty *prop );
-const char *BPy_IDProperty_Map_ValidateAndCreate(const char *name, struct IDProperty *group, PyObject *ob);
+const char *BPy_IDProperty_Map_ValidateAndCreate(PyObject *key, struct IDProperty *group, PyObject *ob);
 
 void IDProp_Init_Types(void);