fixing Strict standards: Declaration of Doctrine_Connection_Mysql::replace() should be compatible with that of Doctrine_Connection::replace()

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Fixed OFFSET clause generation of Pgsql driver, which added the OFFSET keyword without a value to the SQL query in case of OFFSET 0. fixes #230

fixed declaration of Doctrine_Connection_Pgsql::modifyLimitQuery and Doctrine_Connection_Common::modifyLimitQuery to be the same

Removed getState() and concat() methods from mysql driver, getState() is not needed (it resides at transaction class) and concat is located at mysql expression driver