Bug 1735027: Work around for when inbuilt Number.isInteger is not defined, eg Internet Explorer 11

See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isInteger

behatnotneeded

Change-Id: I2c1b77676e603394ce1a12a88f5d763e40ad5826

htdocs/js/mahara.js

@@ -1013,3 +1013,12 @@ function keytabbinginadialog(dialog, firstelement, lastelement) {
         }
     });
 }
+
+/*
+* fix for Internet Explorer where Number.isInteger is not defined
+*/
+Number.isInteger = Number.isInteger || function(value) {
+    return typeof value === "number" &&
+           isFinite(value) &&
+           Math.floor(value) === value;
+};