added options to specify stack parameters
  * set the pixfrac, pixscale and epochs for the stack with
   --stackpixfrac, --stackpixscale, and --stackepochs.
  * excplicitly allow the template epoch to be included with
   --stacktemplate (this is also implicitly activated when
   you use --stackepochs and include the tempepoch in your
   list of epochs to stack)