Update docs for a bunch of 24.3 changes.

Update docs for a bunch of 24.3 changes.

* doc/emacs/killing.texi (Rectangles): Document copy-rectangle-as-kill.

* doc/emacs/search.texi (Special Isearch): Document the lax space search
feature and M-s SPC.
(Regexp Search): Move main search-whitespace-regexp description to
Special Isearch.
(Replace): Document replace-lax-whitespace.

* doc/emacs/basic.texi (Position Info): Document C-u M-=.
(Moving Point): Document move-to-column.

* doc/emacs/display.texi (Useless Whitespace): Add delete-trailing-lines.

* doc/emacs/misc.texi (emacsclient Options): Document the effect of
initial-buffer-choice on client frames.  Document server-auth-dir.
Do not document server-host, which is bad security practice.

* doc/emacs/building.texi (Lisp Libraries): Docstring lookups can trigger
autoloading.  Document help-enable-auto-load.

* doc/emacs/mini.texi (Yes or No Prompts): New node.

* doc/emacs/ack.texi (Acknowledgments): Remove obsolete packages.

* doc/lispref/commands.texi (Click Events): Define "mouse position list".
Remove mention of unimplemented horizontal scroll bars.
(Drag Events, Motion Events): Refer to "mouse position list".
(Accessing Mouse): Document posnp.

* doc/lispref/errors.texi (Standard Errors): Tweak arith-error description.
Tweak markup.  Remove domain-error and friends, which seem to be
unused after the floating-point code revamp.

* doc/lispref/functions.texi (Obsolete Functions): Obsolescence also affects
documentation commands.  Various clarifications.
(Declare Form): New node.

* doc/lispref/loading.texi (Autoload):
* doc/lispref/help.texi (Documentation Basics): The special sequences can
trigger autoloading.

* doc/lispref/macros.texi (Defining Macros): Move description of `declare' to
Declare Form node.

* doc/lispref/numbers.texi (Integer Basics): Copyedits.
(Float Basics): Consider IEEE floating point always available.
(Random Numbers): Document actual limits.
(Arithmetic Operations): Clarify division by zero.  Don't mention
the machine-independence of negative division since it does not
happen in practice.

* doc/lispref/os.texi (Idle Timers): Minor clarifications.
(User Identification): Add system-users and system-groups.

* doc/lispref/strings.texi (String Basics): Copyedits.

* lisp/minibuffer.el (minibuffer-local-filename-syntax): Doc fix.

* lisp/server.el (server-host): Document the security implications.
(server-auth-key): Doc fix.

* lisp/startup.el (initial-buffer-choice): Doc fix.

* src/fns.c (Frandom): Doc fix.