log for r1850:

Implement this feature request:
http://bugs.mysql.com/30706

* Add a function that returns the number of microseconds since
  epoch - ut_time_us().

* Add (innodb|innobase|srv)_replication_delay MySQL config parameter.

* Add UT_WAIT_FOR() macro that waits for a specified condition to occur
  until a timeout elapses.

* Using all of the above, handle the replication thread specially in
  srv_conc_enter_innodb().