Consolidate all the random code into a random helper that offers:

random::hash()
  random::string()
  random::percent()
  random::int()

So that we don't have lots of different ways to get random values all
over the code.  Follow-on to #1527.

modules/gallery/tests/Albums_Controller_Test.php

@@ -31,7 +31,7 @@ class Albums_Controller_Test extends Gallery_Unit_Test_Case {
     $album = test::random_album();
 
     // Randomize to avoid conflicts.
-    $new_name = "new_name_" . mt_rand();
+    $new_name = "new_name_" . random::string(6);
 
     $_POST["name"] = $new_name;
     $_POST["title"] = "new title";