fix the cat command
- 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
#!/bin/shhg initecho This is file a1 > ahg add ahg commit -m "commit #0" -d "0 0"touch bhg add brm bhg commit -A -m"comment #1" -d "0 0"