Need short array syntax here too

This corresponds to github pull request 777:
https://github.com/facebook/hiphop-php/pull/777

hphp/test/quick/short_array_syntax.php

@@ -0,0 +1,10 @@
+<?php
+function f($x = [1]) {
+  return $x;
+}
+class C {
+  public static $y = [2, 3];
+}
+var_dump([]);
+var_dump(f());
+var_dump(C::$y);

hphp/test/quick/short_array_syntax.php.expect

@@ -0,0 +1,12 @@
+array(0) {
+}
+array(1) {
+  [0]=>
+  int(1)
+}
+array(2) {
+  [0]=>
+  int(2)
+  [1]=>
+  int(3)
+}