Postgres, support ApplicationName config to distinguish db connections

in the server we can use queries such as:

```
SELECT * FROM pg_stat_activity WHERE datname = 'dbname';
```

Author: JesseChavez

lib/arjdbc/postgresql/adapter_hash_config.rb

@@ -13,7 +13,13 @@ def build_connection_config(config)
       port = (config[:port] ||= ENV["PGPORT"] || 5432)
       database = config[:database] || config[:dbname] || ENV["PGDATABASE"]
 
-      config[:url] ||= "jdbc:postgresql://#{host}:#{port}/#{database}"
+      app = config[:application_name] || config[:appname] || config[:application]
+
+      config[:url] ||= if app
+                         "jdbc:postgresql://#{host}:#{port}/#{database}?ApplicationName=#{app}"
+                       else
+                         "jdbc:postgresql://#{host}:#{port}/#{database}"
+                       end
 
       config[:url] << config[:pg_params] if config[:pg_params]