removing lines array cloning to reduce GC-pressure

Originally submitted as past of one big PR #136

This change is the most controversial one, but added as a separate PR for the sake of completeness. As far as I understand the general consensus is to not apply this change no matter how big performance gain we can achieve:
1. Ivan (me) - for applying this PR/further investigation of performance benefits of this particular change
2. Every other maintainer - for rejecting this change due to lack of defending of our internal data-structures from the custom checks.