Put all path conversions in one file
Convert the --tmpdir  passed to "mysqld --verbose --help"


mysql-test/lib/My/Find.pm:
  Use My::Platform
mysql-test/lib/My/SafeProcess.pm:
  use My::Platform
mysql-test/lib/mtr_cases.pm:
  Use My::Platform
mysql-test/lib/mtr_misc.pl:
  Move 'mtr_native_path' to My::Platform
mysql-test/lib/My/Platform.pm:
  New BitKeeper file ``mysql-test/lib/My/Platform.pm''
mysql-test/lib/t/Platform.t:
  New BitKeeper file ``mysql-test/lib/t/Platform.t''