tests/test-merge-force.t

posix, windows: introduce cachestat

This class contains a stat result, and possibly other file info to reliably
determine between two points in time whether a file has changed.

Uniquely identifying a file gives us that reliability because we either
atomic rename or append. So one of two will happen: the file 'id' will change,
or the size of the file will change.

posix implements it simply by calling os.stat() and checking if the result
has st_ino.

For now on Windows we always assume the path is uncacheable. This can be
improved on NTFS due to file IDs: http://msdn.microsoft.com/en-us/library/aa363788(v=vs.85).aspx

So we need to find out if a file path is on an NTFS drive, for that we have:

- GetVolumeInformation, which unfortunately only works with a root path (but is available on XP)
- GetVolumeInformationByHandleW, works on a full file path but requires Vista or higher

  $ hg init

  $ echo a > a
  $ hg ci -qAm 'add a'

  $ echo b > b
  $ hg ci -qAm 'add b'

  $ hg up -qC 0
  $ hg rm a
  $ hg ci -m 'rm a'
  created new head

  $ hg up -qC 1
  $ rm a

Local deleted a file, remote removed

Should fail, since there are deleted files:

  $ hg merge
  abort: outstanding uncommitted changes (use 'hg status' to list changes)
  [255]

Should succeed with --force:

  $ hg -v merge --force
  resolving manifests
  removing a
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

Should show 'a' as removed:

  $ hg status
  R a

  $ hg ci -m merge

Should not show 'a':

  $ hg manifest
  b