static deltas status

[Colin Walters <walters verbum org>]

Now that we have the summary file covering GPG signatures, I think the last major *known* blocker for me 
calling this stable is finalizing our bsdiff status.  Though bugs continue to be found:
https://bugzilla.gnome.org/show_bug.cgi?id=756260
(Thanks John!)

There's been a background conversation about bsdiff here:

https://lists.clearlinux.org/pipermail/dev/2015-September/000048.html

Having the checksum + fallback fetch (via the base archive-z2) option would help a lot, shouldn't
be too hard to implement.

It'd also be useful to do a diff of https://github.com/mendsley/bsdiff vs what's
in Clear Linux.