return standard SQL values (sqlite3 understands CURRENT_...)

lib/MDB2/Driver/Function/sqlite3.php

@@ -55,12 +55,12 @@ class MDB2_Driver_Function_sqlite3 extends MDB2_Driver_Function_Common
     {
         switch ($type) {
         case 'time':
-            return 'time(\'now\')';
+            return 'CURRENT_TIME';
         case 'date':
-            return 'date(\'now\')';
+            return 'CURRENT_DATE';
         case 'timestamp':
         default:
-            return 'datetime(\'now\')';
+            return 'CURRENT_TIMESTAMP';
         }
     }