krb5: add krb5_store_bytes()

Similar to krb5_storage_write(), but returns an error rather than the number of
bytes written.

lib/krb5/version-script.map

@@ -650,6 +650,7 @@ HEIMDAL_KRB5_2.0 {
 		krb5_store_address;
 		krb5_store_addrs;
 		krb5_store_authdata;
+		krb5_store_bytes;
 		krb5_store_creds;
 		krb5_store_creds_tag;
 		krb5_store_data;