Better handling of up/down arrows for CodeCells.

IPython/frontend/html/notebook/static/js/notebook.js

@@ -88,12 +88,22 b' Notebook.prototype.bind_events = function () {'
     var that = this;
     $(document).keydown(function (event) {
         // console.log(event);
-        if (event.which == 38 && event.shiftKey) {
-            event.preventDefault();
-            that.select_prev();
-        } else if (event.which == 40 && event.shiftKey) {
-            event.preventDefault();
-            that.select_next();
+        if (event.which == 38) {
+            var cell = that.selected_cell();
+            if (cell instanceof CodeCell) {
+                if (cell.at_top()) {
+                    event.preventDefault();
+                    that.select_prev();                    
+                };
+            };
+        } else if (event.which == 40) {
+            var cell = that.selected_cell();
+            if (cell instanceof CodeCell) {
+                if (cell.at_bottom()) {
+                    event.preventDefault();
+                    that.select_next();                    
+                };
+            };
         } else if (event.which == 13 && event.shiftKey) {
             // The focus is not quite working here.
             var cell = that.selected_cell();
@@ -782,6 +792,26 b' CodeCell.prototype.set_code = function (code) {'
 };
 
 
+CodeCell.prototype.at_top = function () {
+    var cursor = this.code_mirror.getCursor();
+    if (cursor.line === 0) {
+        return true;
+    } else {
+        return false;
+    }
+};
+
+
+CodeCell.prototype.at_bottom = function () {
+    var cursor = this.code_mirror.getCursor();
+    if (cursor.line === (this.code_mirror.lineCount()-1)) {
+        return true;
+    } else {
+        return false;
+    }
+};
+
+
 CodeCell.prototype.fromJSON = function (data) {
     if (data.cell_type === 'code') {
         this.set_code(data.code);