fixed by using flush logs, dumping, then doing PURGE MASTER LOGS TO 'binfile', instead
of deleting the log files at the beginning.
  
  NOTE: previously the delete-master-logs  would reset the log names back to
filename.00001. Now the trailing number doesn't get reset. This may need to be
documented. 


client/mysqldump.c:
  changed the code the --delete-master-logs option is used from this:
      
      take locks
      delete bin logs
      do dump (if this is a lock-based dump)
      release locks
      do dump (if this is a consistent-read-dump)
      
   to this:
      
      take locks
      flush logs
      remember the name of the new log
      do dump (if this is a lock-based dump)
      release locks
      do dump (if this is a consistent-read-dump)
      fflush output sql file if specified, to ensure the backup is commited to disk
      --- yes, dump succeeded ---
      do PURGE MASTER LOGS TO up to the new log