- Made it easy to configure the path of the rsync executable.

- Made it easy to configure the path of the rsync executable.
- Fully parse all legal options that might come from a stock rsync and
  validate/restrict any option's args (previously we rejected options
  with args).
- Made it easy to disable specific options.
- Properly handle a multi-arg copy's multiple args.
- Make sure that the restricted dir actually exists and we can chdir
  to it.
- Just reject any dangerous args that have .. in them instead of trying
  to munge them.
- We don't treat single-or double-quotes specially, just backslash-
  escaped characters.
- Turn on strict mode.
- Use the array-arg version of exec() so that we don't spawn a shell.
- Use File::Glob to glob wildcards in args.
- Tweaked the log-file format so that it logs the modified command
  without any "OK" suffix.