Fix inadverent change in Sql_alloc

For placement new, throw() exception specification was removed by accident in 8fe04a3 , making debug tests, that simulate out-of-memory situations, fail (e.g filesort_debug)

Author: vaintroub

sql/sql_alloc.h

@@ -37,7 +37,7 @@ class Sql_alloc
  }
  static void *operator new[](size_t size, MEM_ROOT *mem_root) throw ()
  { return alloc_root(mem_root, 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 alloc_root(mem_root, size); }
  static void operator delete(void *ptr, size_t size) { TRASH(ptr, size); }
  static void operator delete(void *, MEM_ROOT *){}