Make memory_profiler work with Python 2.7 tracemalloc

The tracemalloc module can be made to work on Python 2.7 with [the project providing patches against the Pyithon 2.7 source code](http://pytracemalloc.readthedocs.io/install.html#manual-installation). These two changes make `memory_profiler.py` work with tracemalloc on Python 2.

Author: mjpieters

memory_profiler.py

@@ -48,6 +48,7 @@
 
 if PY2:
     import __builtin__ as builtins
+    from future_builtins import filter
 else:
     import builtins
 
@@ -1122,11 +1123,11 @@ def exec_with_profiler(filename, profiler, backend, passed_args=[]):
     ns = dict(_CLEAN_GLOBALS, profile=profiler)
     _backend = choose_backend(backend)
     sys.argv = [filename] + passed_args
+    if _backend == 'tracemalloc' and has_tracemalloc:
+        tracemalloc.start()
     if PY2:
         execfile(filename, ns, ns)
     else:
-        if _backend == 'tracemalloc' and has_tracemalloc:
-            tracemalloc.start()
         try:
             with open(filename) as f:
                 exec(compile(f.read(), filename, 'exec'), ns, ns)