Fix the SEGFAULT issue we see on some systems when running C tests
in PARALLEL mode.

* subversion/tests/svn_test_main.c
  (test_params_t,
   test_thread): Count the number of tests actually being executed
                 to verify we don't skip them as part of the APR
                 thread pool termination.
  (do_tests_concurrently): Explicitly terminate the threads in the
                           thread pool as APR pool cleanup appears
                           to be unreliable here.  Also compare the
                           number tests actually executed with the
                           total number of tests.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1545651 13f79535-47bb-0310-9956-ffa450edef68