Add a metadata() method to Node, File, Symlink, and Dir VFS objects.

The current implementation just populates the self._metadata field of
all of the objects in a directory (and of directory itself) from the
relevant .bupm file whenever metadata() is called on any one of those
objects.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Reviewed-by: Zoran Zaric <zz@zoranzaric.de>
Reviewed-by: Gabriel Filion <lelutin@gmail.com>
Check for a Node's parent before trying to print its name in __repr__.

Signed-off-by: Martin Zimmermann <info@posativ.org>
Reviewed-by: Zoran Zaric <zz@zoranzaric.de>
[rlb@defaultvalue.org: Edit commit message.]
Don't assume that the tester's $top_dir will sort (via ls -a) before tmp/.

Thanks to Alexander Barton <alex@barton.de> for reporting the problem.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Tested-by: Alexander Barton <alex@barton.de>
Add instructions for CentOS 6 to README.md.

Thanks to Paul Schulz <pschulz01@gmail.com> for the information.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Add missing "install" argument to yum command in README.md.

Thanks to Paul Schulz <pschulz01@gmail.com> for pointing it out.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Add traverse_ref and traverse_objects to git.CatPipe
Add a bup push command
Add documentation for bup push
Add testcase for bup push