[Axiom-developer] configure test for bibtext

[Gabriel Dos Reis]

Ralf --

  There is no intrinsic logical reasons why I did not check for all
other tools that may be bundled with a LaTeX distribution.  
The only reason why I tested only for latex and makeindex is because
those seemed to be the only LaTeX-releated tools used by the current
build system.  Patches that extend the tests to pdflatex, bibtex and friends
are welcome.

Thanks,

-- Gaby