Fix a bug where customizing LaTeX-math-list had no effect until restarting
emacs.

* latex.el (LaTeX-math-initialize): Refactor top-level code into
function.
(LaTeX-math-list): Call `LaTeX-math-initialize' when setting the
value in order to update the key bindings.
Also shuffle around several definitions in order to get a
declaration-before-use order.
Don't prompt for reference format when RefTeX is active.

* latex.el (TeX-arg-ref): New function.

* doc/auctex.texi: Replace occurrences of `TeX-arg-label' with
`TeX-arg-ref'.
(Adding Macros): Document `TeX-arg-ref'.

* style/fancyref.el ("fancyref"): Use `TeX-arg-ref' instead of
`TeX-arg-label'.

* style/latexinfo.el ("latexinfo"): Ditto.

* style/nameref.el ("nameref"): Ditto.

* style/varioref.el ("varioref"): Ditto.

* style/subfigure.el ("subfigure"): Use `TeX-arg-ref' instead of
`TeX-arg-label' and fix parentheses.