Add code suggested by Michal Januszewski <michalj@gmail.com> to ensure that Python tests run correctly even when a previous version of the library is already installed.  I was unable to reproduce his problem on my machine but the fix seems harmless enough.
Add code suggested by Michal Januszewski <michalj@gmail.com> to ensure that
Python tests run correctly even when a previous version of the library is
already installed.  I was unable to reproduce his problem on my machine but
the fix seems harmless enough.



git-svn-id: 54a00c96d7caad0f188abf6e0ebede48f6547068@42 630680e5-0e50-0410-840e-4b1c322b438d

tdfischer/protobuf,tdfischer/protobuf,tdfischer/protobuf,tdfischer/protobuf,tdfischer/protobuf