make-secnet-sites: Handle `pub rsa1' properties specially

make-secnet-sites: Handle `pub rsa1' properties specially

We construct these as a special kind of `rsakey' object, rather than
`pubkey' objects.  This means they will be written out to sites files
the way rsa1 keys are: ie in v1, using `pubkey' rather than `pub' in
sites files and using the rsa-public verb rather than make-public.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>