Some systems show "Thu Jan 01" instead of "Thu Jan 1", which breaks tests.
Using "1000000" yields "Mon Jan 12 13:46:40 1970", which looks the same on
all systems.
- this should allow better detection of removed file
when walking in the history (like hg log)
it doesn't help for the fast path of hg log where
we only look at the filelog
- users of the changelog file list shouldn't assume
anymore that the file still exist (anyway it won't
be found in the manifest like in 2e92bd60edac)
- fix the tests (some hashes changed)
- improve localrepo.walk when passed a node
- make the differents walk commands in commands.py accept a node
- change commands.cat to walk over a revision
- add a test
