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Add a fast version of the testsuite

The idea is to have a way to run as much of the testsuite as possible
in a short time, so that we'll run it more often (such as just before
checking in a change, for example).  'make fast' tries for good
coverage without using too many cycles.  Currently it takes about 4
minutes on a fast machine with an optimised GHC build; I think this
might still be a little on the slow side.

When you say 'make fast' in testsuite/tests/ghc-regress, we run each
test only one way, and all of the long-running tests are omitted.
Also, to get the runtime down further, I arbitrarily omitted many of
the should_run tests (because these tend to take a lot longer than
should_compile or should_fail tests).  I tried to keep a
representative few in each category.

add test for array crash

remove dependencies on hslibs packages

Revamp the testsuite framework.  The previous framework was an
experiment that got a little out of control - a whole new language
with an interpreter written in Haskell was rather heavyweight and left
us with a maintenance problem.

So the new test driver is written in Python.  The downside is that you
need Python to run the testsuite, but we don't think that's too big a
problem since it only affects developers and Python installs pretty
easily onto everything these days.

Highlights:

  - 790 lines of Python, vs. 5300 lines of Haskell + 720 lines of
    <strange made-up language>.

  - the framework supports running tests in various "ways", which should
    catch more bugs.  By default, each test is run in three ways:
    normal, -O, and -O -fasm.  Additionally, if profiling libraries
    have been built, another way (-O -prof -auto-all) is added.  I plan
    to also add a 'GHCi' way.

    Running tests multiple ways has already shown up some new bugs!

  - documentation is in the README file and is somewhat improved.

  - the framework is rather less GHC-specific, and could without much
    difficulty be coaxed into using other compilers.  Most of the
    GHC-specificness is in a separate configuration file (config/ghc).

Things may need a while to settle down.  Expect some unexpected
failures.

Fix these tests.

Rename some functions used in vanilla-test.T to be more consistent/logical.

Add array tests.