Fix scrollbar position in menu when moving up and down with keyboard

fixes #154

Author: mmhooge

js/bootstrap-combobox.js

@@ -327,17 +327,34 @@
         case 38: // up arrow
           e.preventDefault();
           this.prev();
+          this.fixMenuScroll();
           break;
 
         case 40: // down arrow
           e.preventDefault();
           this.next();
+          this.fixMenuScroll();
           break;
       }
 
       e.stopPropagation();
     }
-
+  
+  , fixMenuScroll: function(){
+      var active = this.$menu.find('.active');
+      if(active.length){
+    	  var top = active.position().top;
+    	  var bottom = top + active.height();
+    	  var scrollTop = this.$menu.scrollTop();
+    	  var menuHeight = this.$menu.height();
+    	  if(bottom > menuHeight){
+    		  this.$menu.scrollTop(scrollTop + bottom - menuHeight);
+    	  } else if(top < 0){
+    		  this.$menu.scrollTop(scrollTop + top);
+    	  }
+      }
+  }
+  
   , keydown: function (e) {
       this.suppressKeyPressRepeat = ~$.inArray(e.keyCode, [40,38,9,13,27]);
       this.move(e);