wt-status: tolerate dangling marks

When a user checks out the upstream branch of HEAD, the upstream branch
not being a local branch, and then runs "git status", like this:

  git clone $URL client
  cd client
  git checkout @{u}
  git status

no status is printed, but instead an error message:

  fatal: HEAD does not point to a branch

(This error message when running "git branch" persists even after
checking out other things - it only stops after checking out a branch.)

This is because "git status" reads the reflog when determining the "HEAD
detached" message, and thus attempts to DWIM "@{u}", but that doesn't
work because HEAD no longer points to a branch.

Therefore, when calculating the status of a worktree, tolerate dangling
marks. This is done by adding an additional parameter to
dwim_ref() and repo_dwim_ref().

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/reset.c

@@ -423,7 +423,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 			char *ref = NULL;
 			int err;
 
-			dwim_ref(rev, strlen(rev), &dummy, &ref);
+			dwim_ref(rev, strlen(rev), &dummy, &ref, 0);
 			if (ref && !starts_with(ref, "refs/"))
 				ref = NULL;