Fixed #32316 -- Deferred accessing __file__.

Deferred accessing the module-global variable __file__ because the
Python import API does not guarantee it always exists—in particular, it
does not exist in certain "frozen" environments. The following changes
advanced this goal.

Thanks to Carlton Gibson, Tom Forbes, Mariusz Felisiak, and Shreyas
Ravi for review and feedback.

tests/version/tests.py

@@ -1,17 +1,37 @@
+from unittest import skipUnless
+
+import django.utils.version
 from django import get_version
 from django.test import SimpleTestCase
-from django.utils.version import get_complete_version, get_version_tuple
+from django.utils.version import (
+    get_complete_version, get_git_changeset, get_version_tuple,
+)
 
 
 class VersionTests(SimpleTestCase):
 
     def test_development(self):
+        get_git_changeset.cache_clear()
         ver_tuple = (1, 4, 0, 'alpha', 0)
         # This will return a different result when it's run within or outside
         # of a git clone: 1.4.devYYYYMMDDHHMMSS or 1.4.
         ver_string = get_version(ver_tuple)
         self.assertRegex(ver_string, r'1\.4(\.dev[0-9]+)?')
 
+    @skipUnless(
+        hasattr(django.utils.version, '__file__'),
+        'test_development() checks the same when __file__ is already missing, '
+        'e.g. in a frozen environments'
+    )
+    def test_development_no_file(self):
+        get_git_changeset.cache_clear()
+        version_file = django.utils.version.__file__
+        try:
+            del django.utils.version.__file__
+            self.test_development()
+        finally:
+            django.utils.version.__file__ = version_file
+
     def test_releases(self):
         tuples_to_strings = (
             ((1, 4, 0, 'alpha', 1), '1.4a1'),