Clip bad data points while fitting in MeasureApCorrTask.
Classification: set flux ratio for flux.gaussian

flux.gaussian (the default model) has a wider psf/model than
CModel.  Setting the flux ratio to be appropriate for the
default.
Merge branch 'tickets/HSC-982'
untabify
MeasureApCorrTask: perform final fit after clipping, and log result

Without a final fit, the last clipping iteration was useless.
Logging the result (RMS and number used) assures the user it's working.
MeasureApCorrTask: add flag for sources used in fitting

Flag is "apcorr.<measurement>.used".
tests: add test for MeasureApCorrTask

Includes a test for the recently-introduced clipping behavior.
Merge branch 'tickets/HSC-993'
allow Approx to be selected for background.
Merge branch 'u/bick/HSC-145'
fix error propagation bug in aperture corection