Removed wrong fix for bug #14009 (use of abs() on null value causes problems with filesort)
Mark that add_time(), time_diff() and str_to_date() can return null values


myisam/mi_check.c:
  keyoffset is not a position (no %lx here)
mysql-test/r/func_sapdb.result:
  Fixed test after marking that timediff() can return NULL
sql/item_func.cc:
  Removed wrong fix for bug #14009 (use of abs() on null value causes problems with filesort)
sql/item_timefunc.cc:
  Mark that add_time and str_to_date() can return null values
sql/item_timefunc.h:
  Mark that time_diff can return 0
sql/spatial.cc:
  Simple cleanups during review of new code