resolve https://issues.apache.org/jira/browse/AMQ-3075 - a constraint name needs to be provided for postgres but this is not the general case. extracted the end of the alter statement to allow the postgress adapter to override and provided accessor for the constraint name in case of auto generation issues
activemq/trunk/activemq-core/src/main/java/org/apache/activemq/store/jdbc/Statements.java