Remove the dual-callback scheme for numeric and pointer thread IDs,

deprecate the original (numeric-only) scheme, and replace with the
CRYPTO_THREADID object. This hides the platform-specifics and should reduce
the possibility for programming errors (where failing to explicitly check
both thread ID forms could create subtle, platform-specific bugs).

Thanks to Bodo, for invaluable review and feedback.

crypto/ecdsa/ecdsatest.c

@@ -490,7 +490,7 @@ err:
 	if (ret)
 		ERR_print_errors(out);
 	CRYPTO_cleanup_all_ex_data();
-	ERR_remove_state(0);
+	ERR_remove_thread_state(NULL);
 	ERR_free_strings();
 	CRYPTO_mem_leaks(out);
 	if (out != NULL)