ppStack request for non-convolving and non-rejection options

[Michael Wood-Vasey]

This is a request for ppStack to have a non-convolving option and a non-rejection option. It would be helpful to have options to essentially use ppStack to be able to also median combine or variance-weighted combine images just on a pixel-by-pixel basis.

Mark Huber and Armin Rest have found that they can get good ppSub subtractions with SWarp stacking of pswarp images. It would be good to duplicate the SWarp trivial stacking behavior and then turn on more and more features of ppStack to understand the behavior and where we should tune it for the survey.

This is a high-priority issue for the Transient Classification Server and MOPS efforts.

[Paul Price]

Added this feature on trunk, r23577.

The behaviour is controlled by the PPSTACK recipe:

• Convolution can be turned off by setting CONVOLVE = FALSE.
• All rejection can be turned off by setting ITER = 0.