#14 test log files can can clobbered when the pid wraps

[Danny Faught]

The tool adds the pid of the child process to ensure
that the filename is unique, e.g., test.log.20000. But
when the pid wraps around, existing files could get
clobbered, especially when I hack the code so that old
logs don't get deleted. There should be some protection
against clobbering existing log files.