Use Python concurrency mechanisms that will work with Python 2.7 and Python 3.3

We are using thread module to create worker threads. This module is available in 2.7.* versions of Python but not in 3.* versions.

a) In the short term -- check the default version of Python in install.sh and gracefully exit if it is not 2.7.*

b) In the long term -- use a mechanism that will work with Python 2.7.* as well as Python 3.*