PEP-394 recommends specifying python2 or python3 in shebangs unless the
script is known to only run in an activated virtual environment.
PEP-394 also says distributors may not provide the python command.
Newer versions of Ubuntu, at least, no longer provide python unless the
python-is-python3 package is explicitly installed.
Removed some shebangs from testcases (the test-suite does not need them).
William S Fulton