Factor out code used by packaging commands for HTTP requests (#12169).

We now have one function to prepare multipart POST requests, and we use
CRLF, as recommended by the HTTP spec (#10150).  Initial patch by John
Edmonds.
diff --git a/Misc/ACKS b/Misc/ACKS
index 378b60e..0662bae 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -263,6 +263,7 @@
 Walter Dörwald
 Hans Eckardt
 Rodolpho Eckhardt
+John Edmonds
 Grant Edwards
 John Ehresman
 Eric Eisner