Add -n, -A, -F, --file-type, --numeric-ids and detailed -l to "bup ls".

With the addition of -A, change -a to behave more conventionally,
i.e. to show "." and "..".

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Tested-by: Alexander Barton <alex@barton.de>
Reviewed-By: Zoran Zaric <zz@zoranzaric.de>
[rlb@defaultvalue.org: fall back to n.mode when n.metadata() isn't
 available in node_info() so that CommitDirs ("ls -AF /"), etc. will
 still work; thanks to Gabriel Filion <gabster@lelutin.ca> for the
 report; fix the rdiff-backup test to use -A.]
Signed-off-by: Rob Browning <rlb@defaultvalue.org>