Teach `package-install-file' to install previously rejected tarballs

Whilst Emacs can open the varieties of tarballs with no problem, the
package management functions depended on a particular table layout in
the tarball to calculate the directory for the package.

For example, with BSD tar: `tar cf ...` would generate a rejected
tarball, and `tar cof ...` would generate an accepted one.

* lisp/emacs-lisp/package.el (package-untar-buffer): Compare against
the header name from the tarball rather than the filesystem
expanded form.
(package-tar-file-info): Also allow the first entry to be a plain
directory name without trailing path separator.
---
 lisp/emacs-lisp/package.el | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/lisp/emacs-lisp/package.el b/lisp/emacs-lisp/package.el
index 4268f7d27a..cc371fbc50 100644
--- a/lisp/emacs-lisp/package.el
+++ b/lisp/emacs-lisp/package.el
@@ -926,11 +926,12 @@ package-untar-buffer
   (let ((regexp (concat "\\`" (regexp-quote (expand-file-name dir)) "/"))
         (case-fold-search (file-name-case-insensitive-p dir)))
     (dolist (tar-data tar-parse-info)
-      (let ((name (expand-file-name (tar-header-name tar-data))))
+      (let* ((header-name (tar-header-name tar-data))
+             (name (expand-file-name header-name)))
         (or (string-match regexp name)
             ;; Tarballs created by some utilities don't list
             ;; directories with a trailing slash (Bug#13136).
-            (and (string-equal dir name)
+            (and (string-equal dir header-name)
                  (eq (tar-header-link-type tar-data) 5))
             (error "Package does not untar cleanly into directory %s/" dir)))))
   (tar-untar-buffer))
@@ -1192,8 +1193,10 @@ package-tar-file-info
   "Find package information for a tar file.
 The return result is a `package-desc'."
   (cl-assert (derived-mode-p 'tar-mode))
-  (let* ((dir-name (file-name-directory
-                    (tar-header-name (car tar-parse-info))))
+  (let* ((header-name (tar-header-name (car tar-parse-info)))
+	 (dir-name (or (file-name-directory header-name)
+                       ;; Some tar utilities generate a plain directory name first
+                       (file-name-as-directory header-name)))
          (desc-file (package--description-file dir-name))
          (tar-desc (tar-get-file-descriptor (concat dir-name desc-file))))
     (unless tar-desc
2.38.0