* Check fragment removal error code in prepare phase. It is possible
that the transaction gets BF aborted during fragment removal.
* Mark fragment certified in certify_fragment() even if the provider
returns cert failed error. With current wsrep-API error codes
it may not be possible to distinquish certification failure
and BF abort during fragment replication. This may also be a
provider bug. As a result rollback fragment may sometimes be
replicated when it would not be necessary.
quite useful as there might not be enough information for it
after the statement has been processed. Better to handle retrying
on DBMS side. Also removed after_statement_result enumeration and
return plain int from after_statement().
