delta-show: Don't dump whole superblock, do show fallback checksums
delta-show: Don't dump whole superblock, do show fallback checksums

Doing `g_variant_print (superblock)` is unreadable and not very useful,
since we show the checksums as byte arrays.

However, do show the checksums for fallback objects. This makes it easier to see
which objects are fallbacks (and inspect why).

Closes: #678
Approved by: giuseppe

GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree