Teach the test driver to pass a specific FSFS version number to the test
cases. This doesn't actually do anything at the moment, but the idea is
to, at some point, make the test cases use pre-cooked repositories that
were created by older released versiond of Subversion.

* build/run_tests.py
  (TestHarness.__init__): Parse the FSFS version from the fs-type argument.
  (TestHarness._run_c_test,
   TestHarness._run_py_test): Pass the FSFS version to the test case.

* subversion/tests/cmdline/svntest/main.py
  (_create_parser): Accept a new int parameter, --fsfs-version.
* subversion/tests/svn_test_main.c
  (test_options_e): Add new enum constant, fsfs_version_opt.
  (cl_options): Declare a new option, --fsfs-version.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1619320 13f79535-47bb-0310-9956-ffa450edef68