Make testing dynlibs on Windows work

[igloo]

In  http://www.haskell.org/pipermail/cvs-ghc/2010-January/052238.html Duncan writes:

Management of shared libs on Windows is going to be a bit of a
pain. For the purposes of testing we will want to just modify the
%PATH% to include the lib dir containing the dlls. This should be
enough for the testsuite, to ensure no regressions.

Ian: could you look at this? We'll want all the dlls installed into
the ghc lib dir I think (or a subdir if you prefer). Then the
testsuite on Windows would need to add that directory to the %PATH%
so that executables generated by ghc will be able to find the dlls.

[igloo]

#3879 is milestoned for 6.14.1, so we can't do this before then.

[igloo]

Done:

Mon May  3 07:08:15 PDT 2010  Ian Lynagh <igloo@earth.li>
  * Make the dynlib tests work on Windows