metadata.py: add a more meaningful repr() to Metadata.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Fix the ls -laAF options with respect to the VFS synthetic directories.

Before this, they wouldn't work in various cases where the VFS was
creating synthetic data (like the top-level branch and commit-list
trees).

Oh, and how about some tests?

Thanks to Gabriel Filion <gabster@lelutin.ca> for reporting the
problem.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>