
psphotSetHeaderNstars : counts N_STARS and writes to a header metadata

psphotReadoutCleanup:
  psphotPSFstatsSources : measure stats for PSF model (e.g., FWHM_MAJ) [readout->analysis]
  psphotMomentsStats    : measure stats based on 2nd moments           [readout->analysis]
  psphotSetHeaderNstars : count stars (& subsets)                      [PSPHOT.HEADER]
  psphotDefineHeader    : moves the values from readout->analysis to PSPHOT.HEADER
  
