delete-directory no longer errors when racing

Problem reported by Glenn Morris for package-test.el (Bug#24714).
* doc/lispref/files.texi (Create/Delete Dirs), etc/NEWS: Document this.
* lisp/files.el (files--force): New function.
(delete-directory): Use it to avoid error in this case.

1 files changed, 3 insertions, 0 deletions

diff --git a/doc/lispref/files.texi b/doc/lispref/files.texi
index 9af5ce967c2..62e0199f1ff 100644
--- a/doc/lispref/files.texi
+++ b/doc/lispref/files.texi
@@ -2855,6 +2855,9 @@ This command deletes the directory named @var{dirname}.  The function
 must use @code{delete-directory} for them.  If @var{recursive} is
 @code{nil}, and the directory contains any files,
 @code{delete-directory} signals an error.
+If recursive is non-@code{nil}, there is no error merely because the
+directory or its files are deleted by some other process before
+@code{delete-directory} gets to them.
 
 @code{delete-directory} only follows symbolic links at the level of
 parent directories.