convert/gnuarch: retrieve known archive names list
This will make possible in a followup patch to prevent
following history that is not reachable because an archive
is unknown to the user.
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
created new head
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)