Don't set thd->is_fatal_error in sql_update for duplicate key errors.


mysql-test/r/sp.result:
  New test case for BUG#13729.
mysql-test/r/sp_trans.result:
  New test case for BUG#14840.
mysql-test/t/sp.test:
  New test case for BUG#13729.
mysql-test/t/sp_trans.test:
  New test case for BUG#14840.
sql/sql_update.cc:
  Don't set thd->is_fatal_error if it's a duplicate key error.