lp:737104 Crash in DTCollation::set in 5.1-micro

and a different fix for lp:736370

cache temporal expression in Item_cache_int, not in Item_string.
invoke get_datetime_value() to create a correct Item_cache_int.
Implement Item_cache_int::clone, as it's a proper constant

mysql-test/r/func_time.result

@@ -1497,3 +1497,7 @@ drop table t1;
 select now() > coalesce(time('21:43:24'), date('2010-05-03'));
 now() > coalesce(time('21:43:24'), date('2010-05-03'))
 1
+create table t1 (f1 timestamp);
+select * from t1 where f1 > f1 and f1 <=> timestampadd(hour, 9 , '2010-01-01 16:55:35');
+f1
+drop table t1;

mysql-test/t/func_time.test

@@ -926,7 +926,7 @@ select * from t1 where 1 and concat(f2)=MAKEDATE(2011, 125);
 drop table t1;
 
 #
-# lp:736791 Crash in make_truncated_value_warningwith LEAST()/GREATEST/COALESCE
+# lp:736791 Crash in make_truncated_value_warning with LEAST()/GREATEST/COALESCE
 #
 create table t1 (f1 timestamp);
 insert into t1 values ('0000-00-00 00:00:00');
@@ -938,3 +938,9 @@ drop table t1;
 #
 select now() > coalesce(time('21:43:24'), date('2010-05-03'));
 
+#
+# lp:737104 Crash in DTCollation::set in 5.1-micro
+#
+create table t1 (f1 timestamp);
+select * from t1 where f1 > f1 and f1 <=> timestampadd(hour, 9 , '2010-01-01 16:55:35');
+drop table t1;

sql/item.cc

@@ -6884,8 +6884,15 @@ void resolve_const_item(THD *thd, Item **ref, Item *comp_item)
   char *name=item->name;			// Alloced by sql_alloc
 
   switch (res_type) {
-  case TIME_RESULT: // will be handled by get_datetime_value()
+  case TIME_RESULT:
+  {
+    bool is_null;
+    Item **ref_copy= ref;
+    get_datetime_value(thd, &ref_copy, &new_item, comp_item, &is_null);
+    if (is_null)
+      new_item= new Item_null(name);
     break;
+  }
   case STRING_RESULT:
   {
     char buff[MAX_FIELD_WIDTH];

sql/item.h

@@ -3035,6 +3035,12 @@ public:
   my_decimal *val_decimal(my_decimal *);
   enum Item_result result_type() const { return INT_RESULT; }
   bool cache_value();
+  Item *clone_item()
+  {
+    Item_cache_int *item= new Item_cache_int(cached_field_type);
+    item->store(this, value);
+    return item;
+  }
 };