IMPALA-719: Output correct SQL in SelectStmt.toSql() if the stmt has not been analyzed.

Change-Id: I76ec5916352ace6aa9de1f90f47c4bbf6d369b93
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1172
Reviewed-by: Marcel Kornacker <marcel@cloudera.com>
Tested-by: jenkins