do not allow editor to scroll up automatically

lib/ace/scrollbar.js

@@ -64,8 +64,6 @@ var ScrollBarV = function(parent, renderer) {
     // make element a little bit wider to retain scrollbar when page is zoomed 
     renderer.$scrollbarWidth = 
     this.width = dom.scrollbarWidth(parent.ownerDocument);
-    renderer.$scrollbarWidth = 
-    this.width = dom.scrollbarWidth(parent.ownerDocument);
     this.fullWidth = this.width;
     this.inner.style.width =
     this.element.style.width = (this.width || 15) + 5 + "px";
@@ -85,12 +83,7 @@ var ScrollBarH = function(parent, renderer) {
     this.element.appendChild(this.inner);
 
     parent.appendChild(this.element);
-
+    
-    // in OSX lion the scrollbars appear to have no width. In this case resize the
-    // element to show the scrollbar but still pretend that the scrollbar has a width
-    // of 0px
-    // in Firefox 6+ scrollbar is hidden if element has the same width as scrollbar
-    // make element a little bit wider to retain scrollbar when page is zoomed 
     this.height = renderer.$scrollbarWidth;
     this.fullHeight = this.height;
     this.inner.style.height =
@@ -181,17 +174,18 @@ var ScrollBarH = function(parent, renderer) {
     // on chrome 17+ for small zoom levels after calling this function
     // this.element.scrollTop != scrollTop which makes page to scroll up.
     this.setScrollTop = function(scrollTop) {
-        if (this.scrollTop != scrollTop) {
+        if (Math.abs(this.scrollTop - scrollTop) > 1) {
             this.skipEvent = true;
-            this.scrollTop = this.element.scrollTop = scrollTop;
+            this.scrollTop = this.element.scrollTop = Math.round(scrollTop);
         }
     };
     this.setScrollLeft = function(scrollLeft) {
-        if (this.scrollLeft != scrollLeft) {
+        if (Math.abs(this.scrollLeft - scrollLeft) > 1) {
             this.skipEvent = true;
-            this.scrollLeft = this.element.scrollLeft = scrollLeft;
+            this.scrollLeft = this.element.scrollLeft = Math.round(scrollLeft);
         }
     };
+    this.scrollTop = this.scrollLeft = 0;
 
 }).call(ScrollBarV.prototype);
 ScrollBarH.prototype = ScrollBarV.prototype;