Bug #1473625: stop cPickle making float dumps locale dependent in protocol 0.

On the way, add a decorator to test_support to facilitate running single
test functions in different locales with automatic cleanup.

Lib/test/test_support.py

@@ -251,6 +251,42 @@ def open_urlresource(url):
     fn, _ = urllib.urlretrieve(url, filename)
     return open(fn)
 
+#=======================================================================
+# Decorator for running a function in a different locale, correctly resetting
+# it afterwards.
+
+def run_with_locale(catstr, *locales):
+    def decorator(func):
+        def inner(*args, **kwds):
+            try:
+                import locale
+                category = getattr(locale, catstr)
+                orig_locale = locale.setlocale(category)
+            except AttributeError:
+                # if the test author gives us an invalid category string
+                raise
+            except:
+                # cannot retrieve original locale, so do nothing
+                locale = orig_locale = None
+            else:
+                for loc in locales:
+                    try:
+                        locale.setlocale(category, loc)
+                        break
+                    except:
+                        pass
+
+            # now run the function, resetting the locale on exceptions
+            try:
+                return func(*args, **kwds)
+            finally:
+                if locale and orig_locale:
+                    locale.setlocale(category, orig_locale)
+        inner.func_name = func.func_name
+        inner.__doc__ = func.__doc__
+        return inner
+    return decorator
+
 #=======================================================================
 # Big-memory-test support. Separate from 'resources' because memory use should be configurable.