aspcud is the recommended solver for OPAM and the `aspcud` package is
now building properly on Darwin. As such, we can remove the special case
for Darwin that required OPAM to fall back to the built-in solver.
The opam package manager relies on external solvers to determine package
management decisions it makes related to upgrades, new installations,
etc.
While, strictly speaking, an external solver is optional, aspcud is
highly recommended in documentation. Furthermore, even having a
relatively small number of packages installed quickly causes the limits
of the interal solver to be reached (before it times out).
Aspcud itself depends on two programs from the same suite: gringo, and
clasp.
On Darwin, Boost 1.55 (and thus Gringo) do not build, so we only support
Aspcud on non-Darwin platforms.
This is a bit scary. The sha of 1.2.2 changed, causing a crash on
download of the url. This updates to the current sha. Opam maintainer
why, oh why, do you change a released version without a version bump??
