Add unit test for HASH-TABLE-TEST

The test ensures that there's no error when HASH-TABLE-TEST is called on a hash
table with a custom equality function. The tests pass, with some caveats:

- I'm only about 70% sure that FINISHES is the right test-predicate to use for
  something like this
- The test suite would consistently fail with non-deterministic segfaults while
  testing the MULTIPROCESSING subtest. This could easily be due to the fact that
  I'm using a FreeBSD machine, and don't have access to a Linux machine at the
  moment -- though I'd be happy to re-run the tests when I do. The test suite
  completed when I commented out the MULTIPROCESSING subtest from the ASD
  file. I don't believe this would have any bearing on whether or not the hash
  table tests should pass

src/tests/normal-tests/hash-tables.lsp

@@ -147,6 +147,7 @@
           (signals error (gethash "foobar" ht))
           (signals error (setf (gethash "foobar" ht) 15))
           (finishes (remhash 3 ht))
+          (finishes (hash-table-test ht))
           (is (null (gethash 1 ht)))
           (finishes (setf (gethash 55 ht) 0))
           (is (= (gethash 13 ht) 0)))))