IntegerDigits doc fix: add missing </dl>
Raise an exception on unmatched <dl> tags in docs

This shows up in mathicsserver, which loads all the documentation.
Merge pull request #159 from bnjones/master

Fix unmatched <dl> tag in IntegerDigits docstring
Merge pull request #157 from sn6uv/sympy073

Sympy 0.7.3
Merge pull request #156 from sn6uv/mathics0.6.1

Mathics 0.6
basic unittesting