tests/test-issue619.t

lfs: override walk() in lfsvfs

In order to fix the missing lfs store after an upgrade, I attempted to walk the
store vfs to hardlink to the upgraded repo's store.  But the custom join()
clashes with the default walk() implementation.  First, 'path=None' blew up in
the regex matcher, because it wanted a string.  But even if that is fixed, the
join to walk the root of the vfs wouldn't match the required xx/xx...xx pattern.

The first cut of this was a copy/paste/tweak of the base implementation, but
this version of walk() hides the internal directories, and treats the vfs as a
flat store.  I think this makes sense because most vfs methods call join() on
input paths, which wants the simple oid format.  It also relieves the caller
from having to deal with bogus files/directories in the store.

https://bz.mercurial-scm.org/619

  $ hg init
  $ echo a > a
  $ hg ci -Ama
  adding a

  $ echo b > b
  $ hg branch b
  marked working directory as branch b
  (branches are permanent and global, did you want a bookmark?)
  $ hg ci -Amb
  adding b

  $ hg co -C 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

Fast-forward:

  $ hg merge b
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -Ammerge

Bogus fast-forward should fail:

  $ hg merge b
  abort: merging with a working directory ancestor has no effect
  [255]

Even with strange revset (issue4465)

  $ hg merge ::.
  abort: merging with a working directory ancestor has no effect
  [255]