Please use the user-specified Python, not the system Python

[shamichatterjee]

In e.g. the mjd script,
#!/usr/bin/python --> #!/usr/bin/env python
That way, the script executes the python I've specified on my path, instead of the system python which doesn't know about modules like astropy.

(Randomly encountered this script while trying to figure out a log-y labeling issue.)