Fix bug with grid date filters

tailbone/templates/grids/filter-components.mako

@@ -177,6 +177,9 @@
                 if (date === null) {
                     return null
                 }
+                if (typeof(date) == 'string') {
+                    return date
+                }
                 // just need to convert to simple ISO date format here, seems
                 // like there should be a more obvious way to do that?
                 var year = date.getFullYear()