Replace fake traceback module with real one from CPython.

lib/traceback.py

-# Copyright 2016 Google Inc. All Rights Reserved.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-"""Print or retrieve a stack traceback."""
-
-
-def print_exc(e):
-  print str(e)

lib/weetest.py

@@ -103,7 +103,7 @@ def _RunOneBenchmark(name, test_func):
   except Exception as e:  # pylint: disable=broad-except
     result.status = 'error'
     print 'ERROR'
-    traceback.print_exc(e)
+    traceback.print_exc()
   else:
     result.status = 'passed'
     ops_per_sec = b.N / b.duration
@@ -123,11 +123,11 @@ def _RunOneTest(name, test_func):
   except AssertionError as e:
     result.status = 'failed'
     print name, 'FAILED'
-    traceback.print_exc(e)
+    traceback.print_exc()
   except Exception as e:  # pylint: disable=broad-except
     result.status = 'error'
     print name, 'ERROR'
-    traceback.print_exc(e)
+    traceback.print_exc()
   else:
     result.status = 'passed'
   finally: