TeX output for long exp-cells is broken

[gunterkoenigsmann]

If exp-cells are long enough to be broken into several lines the TeX output currently is something like:

    e^({very long exponent})

instead of

    e^{very long exponent}

This means only the opening parenthesis is drawn as a superscript.

[gunterkoenigsmann]

Marking this as release-critical since it allows wxMaxima to create wrong high-quality output.

[KubaO]

I'm not sure how easy it is to fix, but it'd certainly be nice for the August release.