Merge pull request 2ndQuadrant#6 from asenyshyn/patch-1

Per @asenyshyn, avoid the subquery against `pg_settings` of just using `current_setting`.

Author: ringerc

audit.sql

@@ -104,7 +104,7 @@ BEGIN
         statement_timestamp(),                        -- action_tstamp_stm
         clock_timestamp(),                            -- action_tstamp_clk
         txid_current(),                               -- transaction ID
-        (SELECT setting FROM pg_settings WHERE name = 'application_name'),
+        current_setting('application_name'),          -- client application
         inet_client_addr(),                           -- client_addr
         inet_client_port(),                           -- client_port
         current_query(),                              -- top-level query or queries (if multistatement) from client