added howards update to keep the zero read saturation pixel value for the output pixel instead of making it zero, #893
added howards update to keep the zero read saturation pixel value for the output pixel instead of making it zero, #893

git-svn-id: cc674101e2b794ddc2100b657215d55256e3fd48@16922 fe389314-cf27-0410-b35b-8c050e845b92

jhunkeler/hstcal,jhunkeler/hstcal,jhunkeler/hstcal