Issue #12646: Add an 'eof' attribute to zlib.Decompress.

This will make it easier to detect truncated input streams.

Also, make zlib's error messages more consistent.
diff --git a/Misc/NEWS b/Misc/NEWS
index 112badf..3c137e0 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -254,6 +254,9 @@
 Library
 -------
 
+- Issue #12646: Add an 'eof' attribute to zlib.Decompress, to make it easier to
+  detect truncated input streams.
+
 - Issue #11513: Fix exception handling ``tarfile.TarFile.gzopen()`` when
   the file cannot be opened.