More dired-x cleanup.
* lisp/dired-x.el (dired-bind-jump, dired-bind-man, dired-bind-info):
Doc fixes. Add :set property, replacing top-level calls.
(dired-vm-read-only-folders, dired-vm): Doc fix (drop v. old VM 4).
(dired-guess-shell-gnutar): Test tar version rather than system-type.
(dired-extra-startup, dired-man, dired-info): Doc fixes.
(dired-clean-up-after-deletion): Use when and dolist.
(dired-jump): Use unless and when.
(dired-virtual): Use line-end-position.
(dired-default-directory-alist): Rename from default-directory-alist.
(dired-default-directory): Update for above name change.
(dired-vm): Drop VM < 5 and simplify.
(dired-buffer-more-recently-used-p): Rewrite.
(dired-filename-at-point): Use when and or.
(dired-x-read-filename-at-point): Rename from read-filename-at-point.
Update callers.
* doc/misc/dired-x.texi (Multiple Dired Directories): Update for rename of
default-directory-alist.
(Miscellaneous Commands): No longer mention very old VM version 4.