shelve: handle shelved node on unfiltered repository
To build a version of shelve that use hiding instead of stripping, we need
shelve to be able to find these revisions. This it does not hurt the bundle
version, so we introduce the necessary code in the relevant place.
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.