BUG#4506 "mysqlbinlog --position --read-from-remote-server has wrong "# at" lines",
BUG#4553 "Multi-table DROP TABLE replicates improperly for nonexistent table" with a test file.
It was not possible to add a test for BUG#4506 as in the test suite we must use --short-form
which does not display the "# at" lines.


client/mysqlbinlog.cc:
  Fix for BUG#4506 "mysqlbinlog --position --read-from-remote-server has wrong "# at" lines"
  when reading a remote binlog, the start position is not always BIN_LOG_HEADER_SIZE (4).
sql/sql_table.cc:
  Fix for BUG#4553 "Multi-table DROP TABLE replicates improperly for nonexistent table"
  we must my_error() _before_ we write to the binlog, so that a meaningful error code is available
  in thd->net.last_errno for storage of the DROP TABLE statement into the binlog.