Update Abbrevs and Dired chapters of Emacs manual.

Update Abbrevs and Dired chapters of Emacs manual.

* dired.texi (Dired Enter, Misc Dired Features): Document
dired-use-ls-dired changes.  Mention quit-window.
(Dired Navigation): Add index entries.
(Dired Visiting): Fix View Mode xref.
(Marks vs Flags): Prefer C-/ binding for undo.
(Subdirectories in Dired): Add xrefs.
(Misc Dired Features): Document some Emacs 24 changes.  Add index
entries.

* abbrevs.texi (Abbrev Concepts): No need to mention abbrev-mode
variable, since it is explained in Minor Modes node.
(Defining Abbrevs): Copyedits.
(Expanding Abbrevs): State default of abbrev-all-caps.  Prefer the
C-/ binding for undo.
(Dabbrev Customization): Add xrefs for case-fold-search and
case-replace.

* dired-xtra.texi (Subdir Switches): Add xref.

* maintaining.texi (VC Directory Commands): Mention quit-window.