Simplify travis matrix.

Travis now considers the  ghc: section as a dimension of the build
matrix. So it's possible to build with multiple versions of GHC without
needing to use hvr's scripts.
.travis.yml: run distributed-process-tests test suites as part of CI.
.travis.yml: Make sure binutils can be located.
Merge pull request #161 from tweag/travis-matrix

Rewrite CI scripts