Throw exceptions from constructor

Documentation shows that exceptions should be thrown from the ctor if the connection isn't successfully established, but that's not how things currently behave. See:

http://www.couchbase.com/docs/couchbase-sdk-php-1.1/api-reference-connection.html#table-couchbase-sdk_php_new_couchbase

Also, there was some question of whether or not getResultCode() should be used instead of an exception handling path.

This shows that getResultCode() and getResultMessage() are deprecated
http://www.couchbase.com/docs/couchbase-sdk-php-1.1/api-reference-summary-errors.html