[MONDRIAN-1867] Syntax error using aliases in the order by clause with M...

...ondrian SQL generated against DB2

Change a3012a4 corrected an issue where the alias was not used in the ORDER BY even if requiresOrderByAlias was true for a dialect.
Once that was fixed DB2, ORDER BY queries started failing.  From tests against DB2 10.2 it appears aliases are permitted in the ORDER BY clause only if they are *unquoted* in the SELECT list.  But expressions are also permitted, so requiresOrderByAlias can be set to false.