FIX little fix for Python 3.3-

Author: demiurg906

memory_profiler.py

@@ -1031,7 +1031,7 @@ def exec_with_profiler(filename, profiler):
             with open(filename) as f:
                 exec(compile(f.read(), filename, 'exec'), ns, ns)
         finally:
-            if tracemalloc.is_tracing():
+            if has_tracemalloc and tracemalloc.is_tracing():
                 tracemalloc.stop()