title: How to add a self-defined unit-engine to arcanist
body: <p>I'm using arc as the tool for code reviewing. The bin/arc is not in the git repo, but I wanna add a test engine in the git repo.
  Thus I create directories test-engine, in the test-engine:</p>
  
  <pre><code>__phutil_library_init__.php
  __phutil_library_map__.php,
  src/PyEngine.php
  </code></pre>
  
  <p>the <strong>phutil_library_init</strong>.php:</p>
  
  <pre><code>    &lt;?php
  
      phutil_register_library('PyEngine', __FILE__);
  
  the __phutil_library_map__.php:
  
      phutil_register_library_map(array(
          '__library_version__' =&gt; 2,
          'class' =&gt;
          array(
            'PyEngine' =&gt; 'src/PyEngine.php',
          ),
          'function' =&gt;
          array(
          ),
          'xmap' =&gt;
          array(
            'PyEngine' =&gt; 'ArcanistUnitTestEngine',
          ),
      ));
  </code></pre>
  
  <p>the .arcconfig:</p>
  
  <pre><code>{
      "phabricator.uri" : "blabla",
      "load" : [
        "test-engine"
      ],
      "unit.engine" : "PyEngine"
  }
  </code></pre>
  
  <p>but when I run arc unit, it reports error:</p>
  
  <pre><code> phutil_register_library_map(array(
        '__library_version__' =&gt; 2,
        'class' =&gt;
        array(
          'PyEngine' =&gt; 'src/PyEngine.php',
        ),
        'function' =&gt;
        array(
        ),
        'xmap' =&gt;
        array(
          'PyEngine' =&gt; 'ArcanistUnitTestEngine',
        ),
      ));[2015-09-08 09:11:55] ERROR 8: Undefined index: PyEngine at [~/Documents/codes/arcanist/libphutil/src/moduleutils/PhutilBootloader.php:136]
      PyEngine(head=dev, ref.master=fc7de2baac4e, ref.dev=615bad5693e1), arcanist(head=master, ref.master=968f4ae5d73e), phutil(head=master, ref.master=55f554b618b9)
        #0 PhutilBootloader::getLibraryMap(string) called at [&lt;phutil&gt;/src/symbols/PhutilSymbolLoader.php:194]
        #1 PhutilSymbolLoader::selectAndLoadSymbols() called at [&lt;phutil&gt;/src/moduleutils/PhutilBootloader.php:78]
        #2 PhutilBootloader::registerLibrary(string, string) called at [&lt;phutil&gt;/src/moduleutils/core.php:4]
        #3 phutil_register_library(string, string) called at [&lt;PyEngine&gt;/__phutil_library_init__.php:3]
        #4 include_once(string) called at [&lt;phutil&gt;/src/moduleutils/PhutilBootloader.php:226]
        #5 PhutilBootloader::executeInclude(string) called at [&lt;phutil&gt;/src/moduleutils/PhutilBootloader.php:207]
        #6 PhutilBootloader::loadLibrary(string) called at [&lt;phutil&gt;/src/moduleutils/core.php:12]
        #7 phutil_load_library(string) called at [&lt;arcanist&gt;/scripts/arcanist.php:611]
        #8 arcanist_load_libraries(array, boolean, string, ArcanistWorkingCopyIdentity) called at [&lt;arcanist&gt;/scripts/arcanist.php:162]
      phutil_register_library_map(array(
        '__library_version__' =&gt; 2,
        'class' =&gt;
        array(
          'PyEngine' =&gt; 'src/PyEngine.php',
        ),
        'function' =&gt;
        array(
        ),
        'xmap' =&gt;
        array(
          'PyEngine' =&gt; 'ArcanistUnitTestEngine',
        ),
      ));[2015-09-08 09:11:55] ERROR 8: Undefined index: PyEngine at [~/Documents/codes/arcanist/libphutil/src/moduleutils/PhutilBootloader.php:136]
      PyEngine(head=dev, ref.master=fc7de2baac4e, ref.dev=615bad5693e1), arcanist(head=master, ref.master=968f4ae5d73e), phutil(head=master, ref.master=55f554b618b9)
        #0 PhutilBootloader::getLibraryMap(string) called at [&lt;phutil&gt;/src/symbols/PhutilSymbolLoader.php:194]
        #1 PhutilSymbolLoader::selectAndLoadSymbols() called at [&lt;phutil&gt;/src/__phutil_library_init__.php:22]
        #2 __phutil_autoload(string)
        #3 spl_autoload_call(string)
        #4 call_user_func_array(array, array) called at [&lt;phutil&gt;/src/console/format.php:7]
        #5 phutil_console_format(string, string) called at [&lt;arcanist&gt;/scripts/arcanist.php:413]
      [2015-09-08 09:11:55] EXCEPTION: (Exception) libphutil v1 libraries are no longer supported. at [&lt;phutil&gt;/src/moduleutils/PhutilBootloader.php:144]
      PyEngine(head=dev, ref.master=fc7de2baac4e, ref.dev=615bad5693e1), arcanist(head=master, ref.master=968f4ae5d73e), phutil(head=master, ref.master=55f554b618b9)
        #0 PhutilBootloader::getLibraryMap(string) called at [&lt;phutil&gt;/src/symbols/PhutilSymbolLoader.php:194]
        #1 PhutilSymbolLoader::selectAndLoadSymbols() called at [&lt;phutil&gt;/src/__phutil_library_init__.php:22]
        #2 __phutil_autoload(string)
        #3 spl_autoload_call(string)
        #4 call_user_func_array(array, array) called at [&lt;phutil&gt;/src/console/format.php:7]
        #5 phutil_console_format(string, string) called at [&lt;arcanist&gt;/scripts/arcanist.php:413]
  </code></pre>
  
  <p>How can I add the unit engine properly?</p>