More unit tests for streaming replication.

include/wsrep/client_context.hpp

@@ -229,6 +229,12 @@ namespace wsrep
             return transaction_.start_transaction(wsh, meta);
         }
 
+        int start_replaying()
+        {
+            assert(mode_ == m_applier);
+            return transaction_.start_replaying();
+        }
+
         void adopt_transaction(wsrep::transaction_context& transaction)
         {
             transaction_.start_transaction(transaction.id());

include/wsrep/transaction_context.hpp

@@ -92,6 +92,8 @@ namespace wsrep
         int start_transaction(const wsrep::ws_handle& ws_handle,
                               const wsrep::ws_meta& ws_meta);
 
+        int start_replaying();
+
         int append_key(const wsrep::key&);
 
         int append_data(const wsrep::const_buffer&);