Prevented --parallel from crashing on Windows.

Since --parallel is documented not to work on Windows, it's better to
ignore it and run without parallelization than to crash. For example
this could simplify cross-platform test scripts.

django/test/runner.py

@@ -211,6 +211,11 @@ def default_test_processes():
     """
     Default number of test processes when using the --parallel option.
     """
+    # The current implementation of the parallel test runner requires
+    # multiprocessing to start subprocesses with fork().
+    # On Python 3.4+: if multiprocessing.get_start_method() != 'fork':
+    if not hasattr(os, 'fork'):
+        return 1
     try:
         return int(os.environ['DJANGO_TEST_PROCESSES'])
     except KeyError:

tests/runtests.py

@@ -236,11 +236,8 @@ def teardown(state):
 
 def actual_test_processes(parallel):
     if parallel == 0:
-        # On Python 3.4+: if multiprocessing.get_start_method() != 'fork':
-        if not hasattr(os, 'fork'):
-            return 1
         # This doesn't work before django.setup() on some databases.
-        elif all(conn.features.can_clone_databases for conn in connections.all()):
+        if all(conn.features.can_clone_databases for conn in connections.all()):
             return default_test_processes()
         else:
             return 1