testing.find_python() uses an invalid environment variable name
The find_python() function in testing.py does a
call where the ``version`` variable is something like 2.4, resulting in an environment variable such as "PYTHON2.4" being looked up. At least in some versions of Bash the dot/period is not a valid character which makes using an environment variable impossible.
The attached patch simple does a
in the appropriate place to overcome this.