Make LaTeX-outline-level work for customized outline-regexp.

* latex.el (LaTeX-outline-level): Make it work for customized
`outline-regexp'.  See bug report
http://permalink.gmane.org/gmane.emacs.auctex.bugs/1648.
Support darwin.

* tex.el (TeX-view-program-list-builtin)
(TeX-view-program-selection): Enable commented code to support
darwin system.
Improve TeX-math-input-method-off-regexp.

* tex.el (TeX-math-input-method-off-regexp): Improve and fix typo.
See bug http://permalink.gmane.org/gmane.emacs.auctex.devel/2468.
Fix a bug in font-latex-add-to-syntax-alist.

* font-latex.el (font-latex-add-to-syntax-alist): Fix a bug in
`font-latex-add-to-syntax-alist' where it modified both the buffer
local and global value of `font-latex-syntax-alist'.
Update README for Git.

* README.GIT: Rename from README.CVS; update contents to Git.