When resolving unqualified name references MySQL was not
   checking what is the item type for the reference. Thus
   e.g a string literal item that has by convention a name
   equal to its string value will also work as a reference to 
   a SELECT list item or a table field.
   Fixed by allowing only Item_ref or Item_field to referenced by
   (unqualified) name.


mysql-test/r/func_gconcat.result:
  Bug #14019: group by converts literal string to column name
   - removed undeterministic testcase : order by a constant 
     means no order.
mysql-test/r/group_by.result:
  Bug #14019: group by converts literal string to column name
   - test case
mysql-test/t/func_gconcat.test:
  Bug #14019: group by converts literal string to column name
   - removed undeterministic testcase : order by a constant 
     means no order.
mysql-test/t/group_by.test:
  Bug #14019: group by converts literal string to column name
   - test case
sql/sql_base.cc:
  Bug #14019: group by converts literal string to column name
   - resolve unqualified by name refs only for real references