Add a simple test case for svn_fs_print_modules.

* subversion/tests/libsvn_fs/fs-test.c
  (test_print_modules): New test case.
  (test_funcs): Register the new test case.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1636757 13f79535-47bb-0310-9956-ffa450edef68