libgnurl, a fork of libcurl used by GNUnet
gnunet: add libgnurl and GnuTLS as dependencies

libgnurl is essential for bootstrapping (needed to download a hostlist).
GnuTLS is needed by gnunet-gns-proxy.

Also sort dependencies alphabetically.
Merge pull request #2438 from falsifian/gnunet_deps

fix GNUnet missing dependencies