Document some Emacs 23.3 changes in manuals.

Document some Emacs 23.3 changes in manuals.

* doc/emacs/macos.texi (Mac / GNUstep Basics): Document
ns-right-alternate-modifier.

* doc/lispref/numbers.texi (Float Basics): Document float-e and float-pi.

* doc/lispref/symbols.texi (Creating Symbols): Using unintern without an
obarray arg is now obsolete.

* doc/lispref/text.texi (Kill Functions, Kill Functions)
(Low-Level Kill Ring, Low-Level Kill Ring): Remove obsolete
YANK-HANDLER args.

* doc/lispref/variables.texi (Defining Variables): Change "pi" example to
"float-pi".