Improve integer file mode options docstrings

Improve integer file mode options docstrings

* lisp/eshell/esh-util.el (eshell-private-file-modes)
(eshell-private-directory-modes):
* lisp/gnus/mail-source.el (mail-source-default-file-modes):
* lisp/printing.el (pr-file-modes):
* lisp/gnus/mm-decode.el (mm-attachment-file-modes):
* lisp/gnus/nnmail.el (nnmail-default-file-modes):
* lisp/recentf.el (recentf-save-file-modes):
* lisp/vc/ediff-init.el (ediff-temp-file-mode):
* lisp/vc/emerge.el (emerge-temp-file-mode): Better document the fact
that these are integer and not octal values.

* lisp/epg.el (epg--start):
* lisp/emacs-lisp/package.el (package-import-keyring): Use octal values
to make the code more self-documenting.

(cherry picked from commit da5df90fadbec9db692ff34abcd28ce5a5b29c2a)