-do not warn about libcurl if we have libgnurl

git-svn-id: https://gnunet.org/svn/gnunet@34723 140774ce-b5e7-0310-ab8b-a85725594a96
-do not modify 'const' argument

git-svn-id: https://gnunet.org/svn/gnunet@34727 140774ce-b5e7-0310-ab8b-a85725594a96