Allow date -s to accept a format specifier

Some examples:
  # Set the date to time_t=1343286000 (which is July 26, 2012)
  date +%s -s 1343286000

  # Set the date to the first day of the year 2012.
  date +%Y -s 2012

Change-Id: I493f98ba6216b59375e999f744ecf2434c606a10
1 file changed