New fluxd2afrho and updates to get running.

util.bandpass uses davint, rather than scipy's trapz.  Also, let
source error be optional.

davint's source files needed some edits to get it to specify some
variables as output.  Not sure why it was working earlier and not now.

calib.filter needed column numbers for MKO, IRAC, MIPS, and IRS filters.
Added comet.fluxd2efrho and m2afrho1.
Merge pull request #12 from mkelley/afrho

Add Afrho functions to comet module.