texvccheck: use texvc as input verification only.

texvc the input language for formulae in wikipedia has become familiar to wide user range of wikipedia editors. Texvc accepts a selection of LaTeX commands augmented with customized macros as user input. In some cases the input is transformed to html or mathml. But in the majority texvc creates a LaTeX document that is rendered via latex to dvi and then converted to an image. The intermediate tex, dvi and aux files are cleaned up accessible after the conversion is completed.