The reported problems were due to two completely unrelated omissions.
1) The file sort procedure didn't correctly create the sort key in
   make_sortkey when the sortkey was an unsigned integer.
2) The name resolution procedure for column references inside a HAVING
   clause did not propagate the unsigned_flag of the resolved references.
This patch corrects both problems.


mysql-test/r/select.result:
  Added test result for BUG#7425.
mysql-test/t/select.test:
  Added test for BUG#7425.
sql/filesort.cc:
  Take into account whether 'item' represents a signed or an unsigned integer.
sql/item.cc:
  Once an Item_ref is resolved, propagate the unsigned_flag to the resolved item.