Moved removeChildren to core.js

The function removeChildren is a general utility that other functions
might want to use.
Fixes #4120. Thanks arvin for the initial patch.

django/contrib/admin/static/admin/js/calendar.js

@@ -1,11 +1,8 @@
 /*
 calendar.js - Calendar functions by Adrian Holovaty
+depends on core.js for utility functions like removeChildren or quickElement
 */
 
-function removeChildren(a) { // "a" is reference to an object
-    while (a.hasChildNodes()) a.removeChild(a.lastChild);
-}
-
 // CalendarNamespace -- Provides a collection of HTML calendar-related helper functions
 var CalendarNamespace = {
     monthsOfYear: gettext('January February March April May June July August September October November December').split(' '),

django/contrib/admin/static/admin/js/core.js

@@ -50,6 +50,11 @@ function quickElement() {
     return obj;
 }
 
+// "a" is reference to an object
+function removeChildren(a) {
+    while (a.hasChildNodes()) a.removeChild(a.lastChild);
+}
+
 // ----------------------------------------------------------------------------
 // Cross-browser xmlhttp object
 // from http://jibbering.com/2002/4/httprequest.html