Fix bug #12298 Typo in timestampdiff() function name results in erroneous

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

@@ -687,7 +687,7 @@ timestampdiff(SQL_TSI_FRAC_SECOND, '2001-02-01 12:59:59.120000', '2001-05-01 12:
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
 Warnings:
-Note	1003	select timestamp_diff(WEEK,_latin1'2001-02-01',_latin1'2001-05-01') AS `a1`,timestamp_diff(SECOND_FRAC,_latin1'2001-02-01 12:59:59.120000',_latin1'2001-05-01 12:58:58.119999') AS `a2`
+Note	1003	select timestampdiff(WEEK,_latin1'2001-02-01',_latin1'2001-05-01') AS `a1`,timestampdiff(SECOND_FRAC,_latin1'2001-02-01 12:59:59.120000',_latin1'2001-05-01 12:58:58.119999') AS `a2`
 select last_day('2005-00-00');
 last_day('2005-00-00')
 NULL

mysql-test/r/view.result

@@ -2092,3 +2092,8 @@ SELECT a FROM v1;
 a
 DROP VIEW v1;
 DROP TABLE t1,t2,t3,t4,t5;
+create view v1 as select timestampdiff(day,'1997-01-01 00:00:00','1997-01-02 00:00:00') as f1;
+select * from v1;
+f1
+1
+drop view v1;

mysql-test/t/view.test

@@ -1936,4 +1936,9 @@ SELECT a FROM v1;
 DROP VIEW v1;
 DROP TABLE t1,t2,t3,t4,t5;
 
-
+#
+# Bug #12298 Typo in  function name results in erroneous view being created.
+#
+create view v1 as select timestampdiff(day,'1997-01-01 00:00:00','1997-01-02 00:00:00') as f1;
+select * from v1;
+drop view v1;

sql/item_timefunc.h

@@ -860,7 +860,7 @@ class Item_func_timestamp_diff :public Item_int_func
 public:
   Item_func_timestamp_diff(Item *a,Item *b,interval_type type_arg)
     :Item_int_func(a,b), int_type(type_arg) {}
-  const char *func_name() const { return "timestamp_diff"; }
+  const char *func_name() const { return "timestampdiff"; }
   longlong val_int();
   void fix_length_and_dec()
   {