Squash a byte-compiler warning.

* latex.el (LaTeX-close-environment): Remove non-interactive
`next-line' usage compile warning.
Advice instead of fset + redefine.

* context.el (ConTeXt-add-environments): Advice instead of
renaming and redefining generated function.

* latex.el (LaTeX-add-bibliographies): Advice instead of
renaming and redefining generated function.
(LaTeX-add-environments): Ditto.
Fix bug causing endless package queries.

* latex.el (LaTeX-arg-usepackage-read-packages-with-options): Fix
bug that caused AUCTeX to query for packages infinitely.