Refs #1448 @15m

refs #1461 @30m

- Was wrongly handled in tsig_add().

refs #1448

refs #1448 @30m

- Modified function xfr_check_tsig() in xfr-handler.c to store
  the extended TSIG RCODE in the xfr_t structure and to store
  client's time signed in case of time error.
- Modified tsig_add() header.
- Handling TSIG errors in ns_xfr_send_and_clear().

refs #1448 @2h

- Modified tsig_sign() to accept TSIG extended RCODE.
- Added new API for adding TSIG without signing.

refs #1448 @1h

refs #1433

Added two more algorithms to tsig. Others can be added later, it's almost too easy, but I would not support all algorithms - bigger probability of an error.

Refs #1406

refs #1362

To do: finish implementation of tsig_rdata_alg().

refs #1406

fixes #1403, #1405

Required for storing remote metadata for TSIG
key extraction.

refs #1403

This reverts commit 68960102.