Enable the manual dist missing workaround

- I suddenly remember that pyinstaller also has this potential issue so
  this might fix that, i.e. when the hook to collect data files for the
  package metadata isn't included, something like the following might be
  usable:

  ```
  from PyInstaller.utils.hooks import collect_data_files, copy_metadata

  datas = []
  datas.extend(collect_data_files("ply"))
  datas.extend(copy_metadata("ply"))
  datas.extend(collect_data_files("calmjs.parse"))
  datas.extend(copy_metadata("calmjs.parse"))
  ```

  Naturally, the pre-generated modules must already be present before
  they can be collected.

- This might fix the issue as reported by the user of yet another non-
  standard Python environment in #42.

src/calmjs/parse/utils.py

@@ -14,11 +14,13 @@
     from pkg_resources import Requirement
     ply_dist = working_set.find(Requirement.parse('ply'))
     # note that for **extremely** ancient versions of setuptools, e.g.
-    # setuptools<0.6c11, will require the following workaround...
-    # if ply_dist is None:
-    #     from pkg_resources import Distribution
-    #     import ply
-    #     ply_dist = Distribution(project_name='ply', version=ply.__version__)
+    # setuptools<0.6c11, or some very non-standard environment that does
+    # not include the required metadata (e.g. pyinstaller without the
+    # required metadata), will require the following workaround...
+    if ply_dist is None:  # pragma: no cover
+        from pkg_resources import Distribution
+        import ply
+        ply_dist = Distribution(project_name='ply', version=ply.__version__)
 except ImportError:  # pragma: no cover
     ply_dist = None