Splitdefinitions is O(n^3) instead of O(n)

[Broes De Cat]

A much more efficient algorithm exists, the Tarjan algorithm to compute Strongly Connected Components. It is already implemented in MinisatID in a related context and could be ported easily to SplitDefinitions. Currently this is not really an issue, but it might become an issue if idp takes ground input or ASP programs with a lot of facts or rules.