BUG#26625: crash in range optimizer (out of mem)

- Define Sql_alloc::operator new() as thow() so that C++ compiler
  handles NULL return values
(there is no testcase as there is no portable way to set limit on the 
amount of memory that a process can allocate)

sql/sql_list.h

@@ -30,7 +30,7 @@
 class Sql_alloc
 {
 public:
-  static void *operator new(size_t size)
+  static void *operator new(size_t size) throw ()
   {
     return (void*) sql_alloc((uint) size);
   }
@@ -38,7 +38,7 @@ public:
   {
     return (void*) sql_alloc((uint) size);
   }
-  static void *operator new(size_t size, MEM_ROOT *mem_root)
+  static void *operator new(size_t size, MEM_ROOT *mem_root) throw ()
   { return (void*) alloc_root(mem_root, (uint) size); }
   static void operator delete(void *ptr, size_t size) { TRASH(ptr, size); }
   static void operator delete(void *ptr, MEM_ROOT *mem_root)