Log message:
Import why3-0.86.1 as wip/why3.

Why3 is a platform for deductive program verification. It provides a rich
language for specification and programming, called WhyML, and relies
on external theorem provers, both automated and interactive, to
discharge verification conditions. Why3 comes with a standard library of
logical theories (integer and real arithmetic, Boolean operations, sets and
maps, etc.) and basic programming data structures (arrays, queues, hash tables,
etc.). A user can write WhyML programs directly and get correct-by-construction
OCaml programs through an automated extraction mechanism. WhyML is also
used as an intermediate language for the verification of C, Java, or Ada programs