Log Message:
Import minisat2-070721 as wip/minisat2.

Despite the NP completeness of the satisfiabilty problem of Boolean
formulas (SAT), SAT solvers are often able to decide this problem in
a reasonable time frame. As all other NP complete problems are reducible
to SAT, the solvers have become a general purpose tool for this
class of problems.

MiniSat is a minimalistic, open-source SAT solver,
developed to help researchers and developers alike to get started on SAT.
Winning all the industrial categories of the SAT 2005 competition,
MiniSat is a good starting point both for future research in SAT, and for
applications using SAT