Avoid accidental execution with shell.

At least one script seems to assume that it is being run with python in the command line (i.e. python script.py instead of ./script.py), so avoid the temptation to run scripts as ./script.py by disabling execution permission.

(This seemed simpler than fixing the scripts to be truly Linux-friendly, since you would not only have to add #! lines but would also have to fix the command line processing issues.)