NixOS/nixpkgs — pull request #2150 by thoughtpolice (2014-04-06 17:23:00+00:00)
Title: boolector: add version 1.5 and 1.6

There are two versions here because beginning with 1.6.0, Boolector has
a more restrictive, unfree license which disallows commercial use.

As a result, Boolector 1.5 is the default 'boolector' expression.