Work around issue with multiplying units when one is dimensionless
Work around issue with multiplying units when one is dimensionless

The issue is reported at astropy/astropy#2377

mwcraig/ccdproc,pulsestaysconstant/ccdproc,crawfordsm/ccdproc,astropy/ccdproc,evertrol/ccdproc,indiajoe/ccdproc