Corrected test case result for the bug#28494.
item_func.h, item_func.cc:
  Corrected function names after fix for the bug#28494.


mysql-test/r/user_var.result:
  Corrected test case result for the bug#28494.
sql/item_func.h:
  Corrected function names after fix for the bug#28494.
sql/item_func.cc:
  Corrected function names after fix for the bug#28494.