o switch to using finalAttrs pattern over rec expression in
mkDerivation call
o use hash over sha256 in calls to fetchers
o remove the build-time dependency on gnumake42; dtools now builds
fine with the latest version of GNU make
o use stdenv's implicit phases that build+install with make
o specify make flags through makeFlags rather than through an
arbitrary attribute
o remove unnecessary make flags
o build with parallelism
o use checkTarget instead of providing a full checkPhase
o clean up meta
