testing utility to fake time for Date::Calc

 Test::MockTime::DateCalc arranges for the functions in Date::Calc to
 follow the Perl level 'time' function, and in particular any fake date/time
 set there by Test::MockTime. The following Date::Calc functions are changed
 .
  System_Clock
  Today
  Now
  Today_and_Now
  This_Year
  Gmtime
  Localtime
  Timezone
  Time_to_Date
 .
 Gmtime, Localtime, Timezone and Time_to_Date are made to default
 to the Perl-level current time. When called with an explicit time
 argument they're unchanged.