Fix a failure in test "func_in" on some 64-bit big-endian hosts in first 5.0.38 builds.

sql/item_cmpfunc.cc:
  Ensure both operands of a comparison are cast to "ulonglong", not just one only.
  Without this, some 64-bit big-endian hosts failed test "func_in" when 5.0.38 builds were started.
  
  Patch provided by Timothy.

sql/item_cmpfunc.cc

@@ -2236,8 +2236,8 @@ int cmp_longlong(void *cmp_arg,
       One of the args is unsigned and is too big to fit into the 
       positive signed range. Report no match.
     */  
-    if (a->unsigned_flag && ((ulonglong) a->val) > LONGLONG_MAX ||
-        b->unsigned_flag && ((ulonglong) b->val) > LONGLONG_MAX)
+    if (a->unsigned_flag && ((ulonglong) a->val) > (ulonglong) LONGLONG_MAX ||
+        b->unsigned_flag && ((ulonglong) b->val) > (ulonglong) LONGLONG_MAX)
       return a->unsigned_flag ? 1 : -1;
     /*
       Although the signedness differs both args can fit into the signed