fixed test case to produce same results on txn-enabled binary.
temporary fix - permanent fix is it make mysqld behave the same with
MyISAM on auto_increment insert after delete from tbl_name regardless
of how the binary was compiled
sql/slave.cc
fixed concurrency bug with log_seq
sql/slave.h
last_log_seq needs to be updated atomically with pos
sql/sql_repl.cc
cleared up comment and fixed concurrency bug