This reverts commit b9a616e1, which
depends on the "bitvec" library. We need to investigate a bit further that
dependency, as it in turns depends on "vector" 0.9.1 or *below*, since
0.10.* removed support for Data.Vector.Unboxed.Safe which it uses.

Signed-off-by: Helga Velroyen <helgav@google.com>
Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>