Error differencing two obs in the same directory

[rlbyrne]

Attempting to run ps_diff_wrapper on two observations in the same FHD directory errors. The error occurs in compare_plot_prep because name_diff_parts is undefined. I found a hack-y workaround by replacing name_diff_parts with fhdtype_diff_parts. This allows the run to complete but saves the outputs to the wrong directory.

For reference, my function call looks like this:
ps_diff_wrapper, ["/path/to/fhd_output"], ["obsid1", "obsid2"], /uvf_input, /png, /refresh_diff, pols=["xx"], /invert_colorbar, data_min_abs=[1e1,1e12]