#15249: Mangle From lines correctly when body contains invalid bytes.

Fix by Colin Su.  Test by me, based on a test written by Petri Lehtinen.
diff --git a/Misc/ACKS b/Misc/ACKS
index 7f22360..a46ee84 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -915,6 +915,7 @@
 Dan Stromberg
 Daniel Stutzbach
 Andreas Stührk
+Colin Su
 Pal Subbiah
 Nathan Sullivan
 Mark Summerfield
diff --git a/Misc/NEWS b/Misc/NEWS
index 0d76a6e..73f058c 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -109,6 +109,9 @@
 Library
 -------
 
+- Issue #15249: BytesGenerator now correctly mangles From lines (when
+  requested) even if the body contains undecodable bytes.
+
 - Issue #15777: Fix a refleak in _posixsubprocess.
 
 - Issue #15199: Fix JavaScript's default MIME type to application/javascript.