Fixed fetch for BLOB e CLOB data types;
Fixed bind null value in parameter;
Fixed bug when counting distinct records with db2

The Yii internal CDbCommandBuilder does not quote the primary key field before inserting it into the SQL. Therefore, the resulting query was like:
SELECT COUNT(DISTINCT "table".id) ...

But it should be:
SELECT COUNT(DISTINCT "table"."id") ...
Merge pull request #4 from Pfarrer/master

Fixed bug when counting distinct records with db2
Merge master into ibm_db2