`setHeader('Set-Cookie', ...)` special-casing can die

Use the cookie APIs or addHeader instead.

doc/CHANGES.rst

@@ -50,6 +50,11 @@ Features Added
 Restructuring
 +++++++++++++
 
+- Removed the special handling of `Set-Cookie` headers in
+  `HTTPResponse.setHeader`. Use the `setCookie`/`appendCookie`/`expireCookie`
+  methods instead, or if low-level control is needed, use `addHeader` instead
+  to get the exact same effect.
+
 - Removed the `App.version_txt.getZopeVersion` API, you can use
   ``pkg_resources.get_distribution('Zope2').version`` instead.
 

src/ZPublisher/HTTPResponse.py

@@ -330,11 +330,6 @@ class HTTPResponse(BaseResponse):
         if not scrubbed:
             name, value = _scrubHeader(name, value)
         key = name.lower()
-        # The following is crazy, given that we have APIs for cookies.
-        # Special behavior will go away in Zope 2.13
-        if key == 'set-cookie':  
-            self.accumulated_headers.append((name, value))
-        else:
         name = literal and name or key
         self.headers[name] = value