Tweak HubServiceMode shutdown.

Add a workaround for strange shutdown behaviour that manifests when
called from JNLP.  Actually the code path that led to this happening
has, I think, been eliminated by changes elsewhere, but the change
is harmless so keep it in.
Remove Archive references in download page.

These pointed at previous versions of the maven website;
they are no longer present on the existing website.
I could point at them on the old astrogrid website, but
(a) I don't really want to encourage use of that site, since it will
disappear one day and (b) I won't be providing the same thing for
future versions.
Version to 1.3-4
Rename signed jar files.

Call them jsamp-version_signed.jar not jsamp_signed-version.jar.
Reword history.

Regularise date formatting.
Note signed/unsigned flavour of distributed jar files.
Add note encouraging upgrade for hub deployers.