use /usr/bin/python, not /usr/bin/python2.4

A bunch of our python programs called out the python2.4 interpreter
explicitly, but that makes no sense.  This commit makes them shebang
/usr/bin/python instead.

Our install procedure rewrote the #! lines to /usr/bin/python so it worked
on systems with different python versions, but this is more correct.

Signed-off-by: Sebastian Kuzminsky <seb@highlab.com>