Adapt style/babel.el to babel 3.9.

* style/babel.el: Update copyright years and specify last `babel'
version supported.
(LaTeX-babel-language-list): Expand language list to all languages
mentioned in the last version of the manual.
(LaTeX-babel-active-languages): Update in order to parse the
`main' option and ignore the modifiers.
(LaTeX-babel-package-options): Turn the variable into a function
because now requires `TeX-read-key-val'.