LaTeX: escape more specials in image filenames

LaTeX: escape more specials in image filenames

* AUTHORS: Bookkeeping.

* NEWS: Add entry for these changes.

* lisp/muse-latex.el (muse-latex-header, muse-latexcjk-header)
  (muse-latex-slides-header, muse-latex-lecture-notes-header): Escape
  specials in the title.  Define a museincludegraphics command, which is
  able to handle escaped special characters in image filenames.  Thanks
  to Karl Berry for providing this.
  (muse-latex-markup-strings): Use museincludegraphics instead of
  includegraphics in all image-related markup.  Move the width
  specification over to the museincludegraphics command, rather than
  specifying it explicitly.  This allows people to change this
  information in their headers.
  (muse-latex-markup-specials-image): Escape backslashes, "#", and pipe
  characters in image filenames.