Ignore sequential duplicate layers when reading v2s1
Ignore sequential duplicate layers when reading v2s1

When a v2s1 image is stored to disk, some of the layer blobs listed in
its manifest may be discarded as.  Account for this.

Start treating a failure to decode v1compat information as a fatal error
instead of trying to fake it.

Tweak how we build the created-by field in history when generating one
from v2s1 information to better match what we see in v2s2 images.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

Closes: #383
Approved by: rhatdan

nalind/buildah-1,rhatdan/buildah,projectatomic/buildah,projectatomic/buildah,nalind/buildah,nalind/buildah-1,projectatomic/buildah,nalind/buildah,nalind/buildah-1,TomSweeneyRedHat/buildah,rhatdan/buildah,TomSweeneyRedHat/buildah,rhatdan/buildah,TomSweeneyRedHat/buildah,ipbabble/buildah,ipbabble/buildah