Slightly revised version of patch #1538956:

Replace UnicodeDecodeErrors raised during == and !=
compares of Unicode and other objects with a new
UnicodeWarning.

All other comparisons continue to raise exceptions.
Exceptions other than UnicodeDecodeErrors are also left
untouched.
diff --git a/Lib/test/exception_hierarchy.txt b/Lib/test/exception_hierarchy.txt
index 58131d7..a03f7bb 100644
--- a/Lib/test/exception_hierarchy.txt
+++ b/Lib/test/exception_hierarchy.txt
@@ -45,3 +45,4 @@
            +-- UserWarning
            +-- FutureWarning
 	   +-- ImportWarning
+	   +-- UnicodeWarning