contrib: add nettle (not used yet)

contrib/src/nettle/SHA512SUMS

+717d694804ed7e7154a89dff17a57173fa78c3330aa7cb289de7f8150872955518847e9ae7d0a1644980ea60367541f49ba63997328b1545d0555a8f4e212137  nettle-2.2.tar.gz

contrib/src/nettle/rules.mak

+# Nettle
+
+NETTLE_VERSION := 2.2
+NETTLE_URL := ftp://ftp.gnu.org/gnu/nettle/nettle-$(NETTLE_VERSION).tar.gz
+
+# PKGS += nettle
+
+$(TARBALLS)/nettle-$(NETTLE_VERSION).tar.gz:
+	$(call download,$(NETTLE_URL))
+
+.sum-nettle: nettle-$(NETTLE_VERSION).tar.gz
+
+nettle: nettle-$(NETTLE_VERSION).tar.gz .sum-nettle
+	$(UNPACK)
+	$(MOVE)
+
+.nettle: nettle
+	cd $< && $(HOSTVARS) ./configure $(HOSTCONF)
+	cd $< && $(MAKE) install
+	touch $@