the Epoch". (With after review fixes).


mysql-test/r/func_time.result:
  Added test for bug #7515 "from_unixtime(0) now returns NULL instead of
  the Epoch".
mysql-test/t/func_time.test:
  Added test for bug #7515 "from_unixtime(0) now returns NULL instead of
  the Epoch".
sql/item_timefunc.cc:
  Item_func_from_unixtime:
   from_unixtime(0) should return Epoch instead of NULL.
sql/item_timefunc.h:
  Item_func_from_unixtime:
   - Removed unused method definition.
   - fix_length_and_dec() should set maybe_null to true since now
     from_unixtime() can return NULL even in case when none of its
     arguments is NULL.