Log Message:
Update ruby-test-unit to 3.1.7.

* pkgsrc change: revive ruby23 support.

## 3.1.7 - 2016-01-17 {#version-3-1-7}

### Fixes

 * Added a missing require.

## 3.1.6 - 2016-01-17 {#version-3-1-6}

It's a Ruby on Rails integration improvement release.

### Improvements

  * Filtered backtrace of power\_assert.
    [GitHub#114]
  * Improved performance to retrieve test defined location.
  * Improved performance to run fixtures in a test.
  * Supported running a test by `yield` in `setup`:

    Before:

        def setup
          @file = File.open("x")
        end

        def teardown
          @file.close
        end

    After:

        def setup
          File.open("x") do |file|
            @file = file
            yield
          end
        end

  * Added `--default-test-path` option that specifies the default path
    that has tests.
  * Made auto runner registration more lazily. Auto runner isn't
    registered automatically until user defines a test. In the
    previous releases, auto runner is registered automatically when
    user defines a test case.
  * Supported specifying a test by location in command line. For
    example, the following command line runs a test that is defined in
    /tmp/test_a.rb at line 10:

        % ruby -r test-unit -e run_test /tmp/test_a.rb:10

### Fixes

  * Fixed a bug that test isn't ran. The test has the same name as
    data driven test that is defined in parent test case.
    [GitHub#115]