Fixing the modal z-index issue + make modal stacking possible

Created by: demike

This one line patch fixes the z-index issue mentioned in: Issue #3217 (closed) It is also related to Issue #4182 (closed). This pull request should be against 2.1.0-wip branch, hope I got it right this time ;)

docs/assets/js/bootstrap-modal.js

@@ -165,7 +165,7 @@
           var doAnimate = $.support.transition && animate
 
           this.$backdrop = $('<div class="modal-backdrop ' + animate + '" />')
-            .appendTo(document.body)
+            .insertAfter(this.$element)
 
           if (this.options.backdrop != 'static') {
             this.$backdrop.click($.proxy(this.hide, this))

js/bootstrap-modal.js

@@ -165,7 +165,7 @@
           var doAnimate = $.support.transition && animate
 
           this.$backdrop = $('<div class="modal-backdrop ' + animate + '" />')
-            .appendTo(document.body)
+            .insertAfter(this.$element)
 
           if (this.options.backdrop != 'static') {
             this.$backdrop.click($.proxy(this.hide, this))