Tracker issue 3487: sre "bytecode" verifier.

This is a verifier for the binary code used by the _sre module (this
is often called bytecode, though to distinguish it from Python bytecode
I put it in quotes).

I wrote this for Google App Engine, and am making the patch available as
open source under the Apache 2 license.  Below are the copyright
statement and license, for completeness.

# Copyright 2008 Google Inc.
#
# 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.

It's not necessary to include these copyrights and bytecode in the
source file.  Google has signed a contributor's agreement with the PSF
already.