Incremental: allow assembly of foreign array.

Incremental:  allow assembly of foreign array.

If a foreign (i.e. not known to be local) array is discovered
by --incremental assembly, we now assemble it.  However we ignore
any name information in the array so as not to potentially create
a name that conflict with a 'local' array.
Also, foreign arrays are always assembled 'read-auto' to avoid writing
anything until the array is actually used.

Signed-off-by: NeilBrown <neilb@suse.de>