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 like so:

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

  data = collect_data_files("calmjs.parse")
  data.extend(copy_metadata("calmjs.parse"))
  ```

- 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