Fix serialization of PostgreSQL time data types (#504)

* Use a non-UTC timezone when testing the PostgreSQL timezone support.
* Fix serialization of time of day values for PostgreSQL
* Fix serialization of PostgreSQL values for "timestamp with time zone" and "time with time zone" fields.

tests/postgresql/usage/TimeZone.cpp

@@ -131,7 +131,8 @@ int TimeZone(int, char*[])
 {
   namespace sql = sqlpp::postgresql;
 
-  auto dbc = sql::make_test_connection();
+  // We use a time zone with non-zero offset from UTC in order to catch serialization/parsing bugs
+  auto dbc = sql::make_test_connection("+1");
 
   dbc.execute("DROP TABLE IF EXISTS tabdatetime;");
   dbc.execute(

tests/postgresql/usage/make_test_connection.h

@@ -51,7 +51,7 @@ namespace sqlpp
     }
 
     // Starts a connection and sets the time zone to UTC
-    inline ::sqlpp::postgresql::connection make_test_connection()
+    inline ::sqlpp::postgresql::connection make_test_connection(const std::string &tz = "UTC")
     {
       namespace sql = sqlpp::postgresql;
 
@@ -69,7 +69,7 @@ namespace sqlpp
         throw;
       }
 
-      db.execute(R"(SET TIME ZONE 'UTC';)");
+      db.execute("SET TIME ZONE " + tz + ";");
 
       return db;
     }