Mention ERR_remove_state() deprecation, and ERR_remove_thread_state(NULL).

     This work was sponsored by Google.

     [Steve Henson]

  *) Add support for policy mappings extension.

     This work was sponsored by Google.

     CRYPTO_THREADID_set_callback() to register a callback that will call

     either CRYPTO_THREADID_set_numeric() or CRYPTO_THREADID_set_pointer().

     Note that ERR_remove_state() is now deprecated, because it is tied

     to the assumption that thread IDs are numeric.  ERR_remove_state(0)

     to free the current thread's error state should be replaced by

     ERR_remove_thread_state(NULL).

     (This new approach replaces the functions CRYPTO_set_idptr_callback(),

     CRYPTO_get_idptr_callback(), and CRYPTO_thread_idptr() that existed in

     OpenSSL 0.9.9-dev between June 2006 and August 2008. Also, if an