Testing, back to back comparision with existing HT in sequential.

[MathiasBartl]

I do think I got a lot of tests for sequentil use.
But I, d like to do a QuickTest where arbitrary operations are made on my hashtable, and the same on an reference implementation, and at each step, the returnvalues are compared.

Doing something similar for concurrent use would ba a bit more difficult, without some before after ordering, but then maybe we could use disjunct keysets for every thread.