* created tests focusing in multi-master conflicts during cascading foreign key
processing
* in row0upd.cc, calling wsrep_row_ups_check_foreign_constraints only when
running in cluster
* in row0ins.cc fixed regression from MW-369, which caused crash with MW-402.test
It is possible for a stored procedure that has an error handler
that catches SQLEXCEPTION to call thd->clear_error() on a thd
that failed certification. And because the error is cleared,
wsrep patch proceeds with the normal path and may try to commit
statements that should actually abort.
This patch catches the situation where wsrep_conflict_state is
still set, but the thd's error has been cleared, and rolls back
the statement in such cases.
