fixed sync bugs in three test cases
added offset argument to sync_with_master to mysqltest to be able to fix sync bugs
added a test case for slave startup with existing master.info
expanded mysql-test-run.sh to be able to run pre-start shell script initializations


client/mysqltest.c:
  added offset argument to sync_with_master
mysql-test/mysql-test-run.sh:
  added option to run master or slave initialization shell script
mysql-test/r/rpl000016.result:
  fixed bug in test case
mysql-test/t/rpl000012.test:
  fixed syncronization bug
mysql-test/t/rpl000013.test:
  fixed sync bug
mysql-test/t/rpl000016.test:
  fixed ambiguous show slave status.
sql/slave.cc:
  fixed bug that broke slave server start with existing master.info,
  Monty's optimization was not chopping off newline from logname.