* tta/perl/Texinfo/Convert/LaTeX.pm (_latex_header): move usepackage
for graphicx, etoolbox and titleps to packages covered by
END_USEPACKAGE.  It is less likely fo users to want to replace these
packages, making CLASS_BEGIN_USEPACKAGE easier to modify.

* doc/texinfo.texi (@LaTeX{} Customization Variables): update.
Incite to change CLASS_BEGIN_USEPACKAGE, but not END_USEPACKAGE.