Fix #9513 to remove relative imports from multiprocessing.

The test suite currently skips test_multiprocessing on Windows
because it fails on finding _multiprocessing in several
win32-specific blocks. Removing the relative import lets this
through and allows the test to run (and pass).
diff --git a/Lib/multiprocessing/connection.py b/Lib/multiprocessing/connection.py
index b632e93..7d565a7 100644
--- a/Lib/multiprocessing/connection.py
+++ b/Lib/multiprocessing/connection.py
@@ -173,7 +173,7 @@
 
 else:
 
-    from ._multiprocessing import win32
+    from _multiprocessing import win32
 
     def Pipe(duplex=True):
         '''