onFocus should respect disabled

Fixes #766

Author: jrochkind

src/jquery.autocomplete.js

@@ -219,6 +219,10 @@
  onFocus: function () {
  var that = this;
 
+ if (that.disabled) {
+ return;
+ }
+
  that.fixPosition();
 
  if (that.el.val().length >= that.options.minChars) {
@@ -270,7 +274,7 @@
  'z-index': options.zIndex
  });
 
- this.options = options; 
+ this.options = options;
  },