fsm-health-win32: force shutdown daemon if worktree root moves

fsm-health-win32: force shutdown daemon if worktree root moves

Force shutdown fsmonitor daemon if the worktree root directory
is moved, renamed, or deleted.

Use Windows low-level GetFileInformationByHandle() to get and
compare the Windows system unique ID for the directory with a
cached version when we started up.  This lets us detect the
case where someone renames the directory that we are watching
and then creates a new directory with the original pathname.

This is important because we are listening to a named pipe for
requests and they are stored in the Named Pipe File System (NPFS)
which a kernel-resident pseudo filesystem not associated with
the actual NTFS directory.

For example, if the daemon was watching "~/foo/", it would have
a directory-watch handle on that directory and a named-pipe
handle for "//./pipe/...foo".  Moving the directory to "~/bar/"
does not invalidate the directory handle.  (So the daemon would
actually be watching "~/bar" but listening on "//./pipe/...foo".
If the user then does "git init ~/foo" and causes another daemon
to start, the first daemon will still have ownership of the pipe
and the second daemon instance will fail to start.  "git status"
clients in "~/foo" will ask "//./pipe/...foo" about changes and
the first daemon instance will tell them about "~/bar".

This commit causes the first daemon to shutdown if the system unique
ID for "~/foo" changes (changes from what it was when the daemon
started).  Shutdown occurs after a periodic poll.  After the
first daemon exits and releases the lock on the named pipe,
subsequent Git commands may cause another daemon to be started
on "~/foo".  Similarly, a subsequent Git command may cause another
daemon to be started on "~/bar".

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>