Support for replaying prepared XA transactions

This patch implments replaying for prepared XA transactions.
Replay may happen in the following cases:

1) The transaction is BF aborted in prepared state and is idle. In
that case, the transaction is handed over to rollbacker for replay.

2) The transaction is BF aborted while executing the
commit (i.e. before or after successful certification). In
which case the transaction replays itself from fragment storage.

3) The transaction is BF aborted while certifying its commit
fragment. This case is handled like replay for streaming transactions,
where the provider is directly involved and re-delivers the last
fragment.

include/wsrep/transaction.hpp

@@ -146,6 +146,8 @@ namespace wsrep
 
         void xa_detach();
 
+        int xa_replay(wsrep::unique_lock<wsrep::mutex>&);
+
         bool pa_unsafe() const { return pa_unsafe_; }
         void pa_unsafe(bool pa_unsafe) { pa_unsafe_ = pa_unsafe; }