Testsuite and validate changes

All, I made the following changes today: * `make accept` now runs all tests for a single way (instead of all ways) * `make test` now runs all tests for a single way (instead of all ways) * `./validate` now runs all tests for a single way (instead of skipping some tests) * Phabricator now runs all tests for a single way (instead of skipping some tests) You can run `make slowtest` in the root directory, or `make slow` in the testsuite directory, to get the old behavior of `make test` back. More information: * https://ghc.haskell.org/trac/ghc/wiki/Building/RunningTests/Running#Speedset... * https://phabricator.haskell.org/D1178 * Note [validate and testsuite speed] in the toplevel Makefile Thanks, Thomas