Impement options --binlog-commit-wait-count and
--binlog-commit-wait-usec.

These options permit the DBA to deliberately increase latency
of an individual commit to get more transactions in each
binlog group commit. This increases the opportunity for
parallel replication on the slave, and can also decrease I/O
load on the master.

The options also make it easier to test the parallel
replication with mysql-test-run.