smurf: Return extinction tau source to caller

smf_correct_extinction now updates the tausrc argument so that
a caller can determine which scheme was used in AUTO mode.
smurf: Add routine translating TAUSRC enum to a string
smurf: MAKEMAP will now store the tausrc in an ADAM parameter

Only the most recent value is stored so if many files are being
processed and they have different extinction modes, because AUTO
sometimes uses CSOFIT and other times uses WVM, the output parameter
value may not be what is expected.
smurf: EXTINCTION now reports which TAUSRC was used

Previously it only did that when it knew before doing the extinction.
Now the tau source is reported after the fact.