Make tests compile again

To do so, add needed imports and update tests to use the new equality
definition. The test now fail when comparing terms with division by
zero - the division is not residualized.
Normalisation fails on division by zero: add testcase
Remove dead code to not maintain it

Otherwise, this code would stop compiling with next commit.
Fix normalization: residualize division by zero
Merge pull request #6 from Blaisorblade/master

Make tests compile again, residualize division by zero