Syntax: cusptm
   Function: Returns calendar date equivalent of cusp time (Gregorian seconds
             or minutes*60.).  Cusp time is stored in various tuples within the
             event .MEM files (e.g. HYP tuple, SYN tuple).

      Input: No command line input.  Program prompts for cusp time (double
             precision real).  Loops for additional input.
             time  =  gregorian seconds; enter negative number to exit program