cmd/upsin: implement ls
cmd/upsin: implement ls

The old command 'ls' was really glob, which confused me constantly.
Rename it to glob and implement a real ls command, approximately.

Change-Id: I98368383e9da8b48817f426fd2dd6b6eafab0576
Reviewed-on: https://upspin-review.git.corp.google.com/1950
Reviewed-by: Eduardo Pinheiro <55040cbb39ba395339ae7940d8da6cd97797a4a8@google.com>

upspin/upspin,upspin/upspin