Two small fixes to make -debug version usable again.

include/my_sys.h:
  Temporaly reverting Monty's optimization of clear_alloc_root() since it makes -debug server
  unusable.
sql/sql_select.cc:
  After merge fix. Now deletion is done outside of handle_select().
  (We fixed the same issue with deletion of LEX::result in 4.1 for prepared statements
   but in more general way).

include/my_sys.h

@@ -738,7 +738,7 @@ extern void my_free_lock(byte *ptr,myf flags);
 #define my_free_lock(A,B) my_free((A),(B))
 #endif
 #define alloc_root_inited(A) ((A)->min_malloc != 0)
-#define clear_alloc_root(A) { (A)->free= (A)->used= (A)->pre_alloc= 0; }
+#define clear_alloc_root(A) bzero((void *) (A), sizeof(MEM_ROOT))
 extern void init_alloc_root(MEM_ROOT *mem_root, uint block_size,
 			    uint pre_alloc_size);
 extern gptr alloc_root(MEM_ROOT *mem_root,unsigned int Size);

sql/sql_select.cc

@@ -232,8 +232,6 @@ int handle_select(THD *thd, LEX *lex, select_result *result)
     result->abort();
     res= 1;					// Error sent to client
   }
-  if (result != lex->result)
-    delete result;
   DBUG_RETURN(res);
 }