view being created.

Item_func_timestamp_diff::func_name() were returning function name as
"timestamp_diff" thus when view was executed function parameters wasn't 
properly recognized and error was raised.


mysql-test/r/func_time.result:
  Fix test result after bugfix #12298
sql/item_timefunc.h:
  Fix bug #12298 Typo in timestampdiff() function name results in wrong view being created.
mysql-test/t/view.test:
  Test case for bug #12298 Typo in timestampdiff()  function name results in erroneous view being created.
mysql-test/r/view.result:
  Test case for bug #12298 Typo in timestampdiff() function name results in erroneous view being created.