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/intern/bpy_operator.c

@@ -380,7 +380,7 @@ static PyObject *pyop_getrna(PyObject *UNUSED(self), PyObject *value)
 {
 	wmOperatorType *ot;
 	PointerRNA ptr;
-	char *opname= _PyUnicode_AsString(value);
+	const char *opname= _PyUnicode_AsString(value);
 	BPy_StructRNA *pyrna= NULL;
 	
 	if (opname==NULL) {
@@ -413,7 +413,7 @@ static PyObject *pyop_getinstance(PyObject *UNUSED(self), PyObject *value)
 	wmOperatorType *ot;
 	wmOperator *op;
 	PointerRNA ptr;
-	char *opname= _PyUnicode_AsString(value);
+	const char *opname= _PyUnicode_AsString(value);
 	BPy_StructRNA *pyrna= NULL;
 
 	if (opname==NULL) {

source/blender/python/intern/bpy_props.c

@@ -1211,7 +1211,7 @@ static StructRNA *pointer_type_from_py(PyObject *value, const char *error_prefix
 	if (!srna) {
 		if (PyErr_Occurred()) {
 			PyObject *msg= PyC_ExceptionBuffer();
-			char *msg_char= _PyUnicode_AsString(msg);
+			const char *msg_char= _PyUnicode_AsString(msg);
 			PyErr_Format(PyExc_TypeError,
 			             "%.200s expected an RNA type derived from PropertyGroup, failed with: %s",
 			             error_prefix, msg_char);