fast-import: Improve robustness when D->F changes provided in wrong order

When older versions of fast-export came across a directory changing to a symlink (or regular file), it would output the changes in the form M 120000 :239821 dir-changing-to-symlink D dir-changing-to-symlink/filename1 When fast-import sees the first line, it deletes the directory named dir-changing-to-symlink (and any files below it) and creates a symlink in its place. When fast-import came across the second line, it was previously trying to remove the file and relevant leading directories in tree_content_remove(), and as a side effect it would delete the symlink that was just created. This resulted in the symlink silently missing from the resulting repository. To improve robustness, we ignore file deletions underneath directory names that correspond to non-directories. This can also be viewed as a minor optimization: since there cannot be a file and a directory with the same name in the same directory, the file clearly can't exist so nothing needs to be done to delete it. Signed-off-by: Elijah Newren <newren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>