* tta/perl/Texinfo/Convert/LaTeX.pm (_protect_latex_text)
(_protect_text): split _protect_text in two, by adding
_protect_latex_text that does only the protection and gets context
information as arguments.

* tta/perl/Texinfo/Convert/LaTeX.pm (_convert): protect in alt=
argument, although it is not required it may help if the LaTeX macro
is redefined.