Fix GH-16137: "Deduplicate" http headers values but Set-Cookie.

Those are meant to have 1 or plus values separated by a comma even
if the client set them separately.

close GH-1

Fix GH-16137: "Deduplicate" http headers values but Set-Cookie.

Those are meant to have 1 or plus values separated by a comma even
if the client set them separately.

close GH-16154

show more ...