bug#25220: tar-untar-buffer doesn't support symlinks

[npostavs]

Severity: wishlist

tar-untar-buffer silently converts symlinks into regular files.  There
might be some portability trouble with supporting them, but at least we
should warn about low fidelity unpacking, as in the patch below.

This initially turned up as a yasnippet bug, because the package's
tarball was using symlinks.  Of course that has to be fixed by avoiding
symlinks (https://github.com/joaotavora/yasnippet/issues/748).

0001-Warn-about-incomplete-untarring-of-link-files.patch
Description: patch