Modified elements

• IFCENTER, FRQOFF1, and FRQOFF2 columns from the FrontEnd table are reversed for each row where IFFLIPS is true. This factorizes the sign issues when dealing with IF2 instead ot IF1,
• The column BAND is read under the name PART for IMB-FITS version lower than 2. Same for REC1 and REC2 read under the names RECEIVER and BAND respectively,
• REFCHAN is patched to correct values (instead of 1) when dealing with continuum backend (1 channel per chunk),
• the columns MJD, INTEGTIM and ISWITCH are compressed if MSET CALIBRATION BAD is NO (this is the default). In this case all rows where ISWITCH is 0 are removed. Two new columns FOREPOIN and BACKPOIN are added as cross pointers between the original and compressed columns. See section  for details.
• the DATE-OBS and DATE-END stamps of each subscan are patched if MSET CALIBRATION MJDINTER is YES. See HELP for details.