Issue #27787: Merge regrtest fixup from 3.5

Lib/test/libregrtest/save_env.py

@@ -268,6 +268,7 @@ class saved_test_environment:
     def __exit__(self, exc_type, exc_val, exc_tb):
         saved_values = self.saved_values
         del self.saved_values
+        support.gc_collect()  # Some resources use weak references
         for name, get, restore in self.resource_info():
             current = get()
             original = saved_values.pop(name)

Misc/NEWS

@@ -29,6 +29,12 @@ Library
 - Issue #12713: Allowed abbreviation of subcommands by end-users for users of
   argparse.
 
+Tests
+-----
+
+- Issue #27787: Call gc.collect() before checking each test for "dangling
+  threads", since the dangling threads are weak references.
+
 
 What's New in Python 3.6.0 alpha 4
 ==================================