Move commands.forget over to using new walk code.
With no names, it now recursively forgets everything, as is the default
behaviour of other commands. And prints the names of all files it
hasn't specifically been told to forget.
+ hg clone http://localhost:20059/ copy
requesting all changes
abort: error: Connection refused
+ echo 255
255
+ ls copy
ls: copy: No such file or directory
+ cat
+ set +x
+ hg clone http://localhost:20059/foo copy2
requesting all changes
abort: HTTP Error 404: File not found
+ echo 255
255
+ set +x