test-obsshelve.t could be merged with test-shelve.t at some point, but
for now I want the comprehensive coverage. Note that obsshelve in
hg-experimental is a fork of shelve, so we're just merging things back
together. The path to graduation from experimental for obsshelve is to
have a better solution around hiding revisions without creating a ton
of markers that'll get exchanged. We've spent a fair amount of time
talking about what that should look like, but in the interim the
experimental-branded obsshelve is a good thing we should have in core.
As a follow-up I'd like to make obsshelve a case of test-shelve.t, but
I thought this would be easier for the initial import.