ecnf printer prints sets with id 0, which is not valid ecnf

[Roel Standaert]

The ground translator generates set ids starting from 0 (in GroundTranslator::translateSet). However, in ecnf, set ids must be larger than 0, because 0 is used to terminate an expression. This causes the ecnf printer to print invalid ecnf.

I have fixed this in my own code by generating ids starting from 1, also changing the isSet and groundset methods accordingly. I don't know if this is an adequate fix, though.

[Broes De Cat]

That is an adequate fix. If you make it a separate commit and push to your repo, I will merge it in the master.

[Roel Standaert]

Changed numbering of sets to start from 1 instead of 0

See issue 247

→ <<cset 5bcbb559a2f0>>

[Broes De Cat]

Fixes #247 Translator has been changed to start set IDs from 1 (easiest fix to keep the interface clean).

→ <<cset 40d5596fa25d>>