if openssl_random_pseudo_bytes doesn't exist, try uniqid

git-svn-id: https://plugins.svn.wordpress.org/wp-identity/trunk@814742 b8457f37-d9ea-0310-8a92-e5e31aec5664
wp-identity -> ufp Identity

git-svn-id: https://plugins.svn.wordpress.org/wp-identity/trunk@814743 b8457f37-d9ea-0310-8a92-e5e31aec5664