cmd/archive: utility for making a dump of a tree
cmd/archive: utility for making a dump of a tree

Worked on my tree, which contains an Access file prohibiting
write/create, a link and a few files and directories.

Change-Id: I0aa6762d860753b2b2277e38700de2c85115b478
Reviewed-on: https://upspin-review.googlesource.com/5400
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@google.com>

upspin/upspin,upspin/upspin