Add support for building different FS versions to the macosx builder.

* tools/buildbot/slaves/svn-x64-macosx/svncheck.sh:
  (check_tests): New function; run all test variants for one RA type
  (check_fsfs_v6, check_fsfs_v4, check_fsx): New predicates.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1639612 13f79535-47bb-0310-9956-ffa450edef68