Sort expected strings in the error messages.

lib/runtime.js

@@ -124,6 +124,7 @@ PEG.Parser.prototype = {
           case 1:
             return failuresExpected[0];
           default:
+            failuresExpected.sort();
             return failuresExpected.slice(0, failuresExpected.length - 1).join(", ")
               + " or "
               + failuresExpected[failuresExpected.length - 1];

test/compiler-test.js

@@ -463,6 +463,13 @@ test("error messages", function() {
     "",
     'Expected "a" but end of input found.'
   );
+
+  var unsortedErrorsParser = PEG.buildParser('start: "b" / "a"');
+  doesNotParseWithMessage(
+    unsortedErrorsParser,
+    "",
+    'Expected "a" or "b" but end of input found.'
+  );
 });
 
 test("error positions", function() {