Specifying the option `--unsafe-links` (or `-l`) to `mpremote mount` will
allow symlinks to be followed in the local directory that point outside of
the base directory path.
For the unsafe case the `path_check()` method of `PyboardCommand` still
checks for a common path but without expanding symlinks. While this check
is currently redundant, it makes the purpose of the method clearer for
possible future uses or extensions.