Change IsNull and NotNull to use ==/!= nullptr in C++11.

Also update gmock_doctor due to Clang wording change.

scripts/gmock_doctor.py

@@ -362,7 +362,7 @@ def _MockObjectPointerDiagnoser(msg):
                r'which is of non-class type \'(.*::)*(?P<class_name>.+)\*\'')
   clang_regex = (_CLANG_FILE_LINE_RE + r'error: member reference type '
                  r'\'(?P<class_name>.*?) *\' is a pointer; '
-                 r'maybe you meant to use \'->\'\?')
+                 r'(did you mean|maybe you meant) to use \'->\'\?')
   diagnosis = """
 The first argument to ON_CALL() and EXPECT_CALL() must be a mock *object*,
 not a *pointer* to it.  Please write '*(%(mock_object)s)' instead of