Fix permissions bugs with setgid directories etc.
* configure.ac (BSD4_2): Remove; no longer needed. * admin/CPP-DEFINES (BSD4_2): Remove. * doc/lispintro/emacs-lisp-intro.texi (Files List): directory-files-and-attributes now outputs t for attribute that's now a placeholder. * doc/lispref/files.texi (Testing Accessibility): Document GROUP arg of file-ownership-preserved-p. (File Attributes): Document that 9th element is now just a placeholder. * doc/lispref/os.texi (User Identification): Document new functions group-gid, group-real-gid. * etc/NEWS: Document changes to file-attributes, file-ownership-preserved-p. Mention new functions group-gid, group-real-gid. * lisp/files.el (backup-buffer): Don't rely on 9th output of file-attributes, as it's now a placeholder. Instead, use the new optional arg of file-ownership-preserved-p. (file-ownership-preserved-p): New optional arg GROUP. Fix mishandling of setuid directories that would cause this function to return t when it should have returned nil. Document what happens if the file does not exist, and when it's not known whether the ownership will be preserved. * lisp/net/tramp-sh.el (tramp-sh-handle-file-ownership-preserved-p): Likewise. (tramp-get-local-gid): Use group-gid for integer, as that's faster and more reliable. * src/dired.c (Ffile_attributes): Return t as the 9th attribute, to mark it as a placeholder. The old value was often wrong. The only user of this attribute has been changed to use file-ownership-preserved-p instead, with its new group arg. * src/editfns.c (Fgroup_gid, Fgroup_real_gid): New functions. Fixes: debbugs:13125
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