Updated a few comments

Removed useless NULL_HTTP_CLIENT.
Extracted mime code from NET_HTTP_CLIENT_REQUEST.response into specific routine.

library/network/http_client/src/spec/null/null_http_client.e

@@ -1,33 +0,0 @@
-note
-	description : "[
-				Instantiate one of the descendant of HTTP_CLIENT
-				then use `new_session' to create a session of http requests
-			]"
-	date        : "$Date$"
-	revision    : "$Revision$"
-
-class
-	NULL_HTTP_CLIENT
-
-inherit
-	HTTP_CLIENT
-
-feature -- Status
-
-	new_session (a_base_url: READABLE_STRING_8): NULL_HTTP_CLIENT_SESSION
-			-- Create a new session using `a_base_url'.
-		do
-			create Result.make (a_base_url)
-		end
-
-note
-	copyright: "2011-2015, Jocelyn Fiat, Javier Velilla, Eiffel Software and others"
-	license: "Eiffel Forum License v2 (see http://www.eiffel.com/licensing/forum.txt)"
-	source: "[
-			Eiffel Software
-			5949 Hollister Ave., Goleta, CA 93117 USA
-			Telephone 805-685-1006, Fax 805-685-6869
-			Website http://www.eiffel.com
-			Customer support http://support.eiffel.com
-		]"
-end

library/network/http_client/src/spec/null/null_http_client_session.e

@@ -1,11 +1,7 @@
 note
 	description : "[
-				HTTP_CLIENT_SESSION represents a session
-				and is used to call get, post, .... request
-				with predefined settings such as 
-					base_url
-					specific common headers
-					timeout and so on ...
+				NULL version of HTTP_CLIENT_SESSION.
+				It is used if no implementation is available (libcurl or net)
 			]"
 	date: "$Date$"
 	revision: "$Revision$"