Part of SF patch #1313939: Speedup charmap decoding by extending
PyUnicode_DecodeCharmap() the accept a unicode string as the mapping
argument which is used as a mapping table.

This code isn't used by any of the codecs yet.
diff --git a/Misc/NEWS b/Misc/NEWS
index 11dd40c..4d35774 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -563,6 +563,11 @@
 
 - Removed PyRange_New().
 
+- Patch #1313939: PyUnicode_DecodeCharmap() accepts a unicode string as the
+  mapping argument now. This string is used as a mapping table. Byte values
+  greater than the length of the string and 0xFFFE are treated as undefined
+  mappings.
+
 
 Tests
 -----