Cross-Origin Resource Sharing initial support

Initial support for the Cross-Origin Resource Sharing specification.
This allows JavaScript to make requests across domain boundaries.

Also reviewed the filter example to get rid of the context and
the generic classes (we can actually use {WSF_REQUEST}.execution_variable
and {WSF_REQUEST}.set_execution_variable).

Links:
* How to enable server-side: http://enable-cors.org/server.html
* Specification: http://www.w3.org/TR/cors/
* Github: http://developer.github.com/v3/#cross-origin-resource-sharing

library/network/protocol/http/src/http_header_names.e

@@ -194,6 +194,23 @@ feature -- Response header name
 			-- Indicates the authentication scheme that should be used to access the requested entity.
 			--| Example: WWW-Authenticate: Basic
 
+feature -- Cross-Origin Resource Sharing
+
+	header_access_control_allow_origin: STRING = "Access-Control-Allow-Origin"
+			-- Indicates whether a resource can be shared based by returning
+			-- the value of the Origin request header in the response.
+			-- | Example: Access-Control-Allow-Origin: http://example.org
+
+	header_access_control_allow_methods: STRING = "Access-Control-Allow-Methods"
+			-- Indicates, as part of the response to a preflight request,
+			-- which methods can be used during the actual request.
+			-- | Example: Access-Control-Allow-Methods: PUT, DELETE
+
+	header_access_control_allow_headers: STRING = "Access-Control-Allow-Headers"
+			-- Indicates, as part of the response to a preflight request,
+			-- which header field names can be used during the actual request.
+			-- | Example: Access-Control-Allow-Headers: Authorization
+
 feature -- Request or Response header name
 
 	header_cache_control:  STRING = "Cache-Control"
@@ -248,7 +265,7 @@ feature -- MIME related
 	header_content_transfer_encoding: STRING = "Content-Transfer-Encoding"
 
 note
-	copyright: "2011-2012, Jocelyn Fiat, Eiffel Software and others"
+	copyright: "2011-2013, Jocelyn Fiat, Eiffel Software and others"
 	license: "Eiffel Forum License v2 (see http://www.eiffel.com/licensing/forum.txt)"
 	source: "[
 			Eiffel Software