major changes to the process for getting files and images to improve efficiency and decrease failures.

Added a check of trans.jmp against the WCS.  Now defaults to use the WCS if trans.jmp is different and issue a warning.
corrected error when computing WCS based offsets to be sure to use 'flipped' images in certain circumstances.
Added a short-circuit so that we don't try getting 'p' files as Single FITS files but only as MEFs.  this is a hack for speed.