Implement and use Java 7 AutoCloseable where relevant

Java 7's AutoCloseable allows the use of the new try-with-resource pattern that automatically does a close() at the end of the try block.

We could implement this interface in our code in a number of places, among them:

• IterableQueryResult
• directory Session

Then code using these could be simplified to avoid a verbose finally block.

We can also make use of AutoCloseable classes now available in Java 7, among them:

• java.sql.Statement
• InputStream, OutputStream, Reader, Writer
• Socket