Re-add list_url for all R packages (#6110)

* r-igraph: find old packages in the archive

Fixes #6104.

* r-irlba: find old packages in the archive

Fixes #6101.

* r-lazyeval: find old packages in the archive

Fixes #6102.

* packages: set list_url for all packages hosted on CRAN

* packages: consistently use the CRAN archive URLs

var/spack/repos/builtin/packages/r-proto/package.py

@@ -31,5 +31,6 @@ class RProto(RPackage):
 
     homepage = "http://r-proto.googlecode.com/"
     url      = "https://cran.r-project.org/src/contrib/proto_0.3-10.tar.gz"
+    list_url = "https://cran.r-project.org/src/contrib/Archive/proto"
 
     version('0.3-10', 'd5523943a5be6ca2f0ab557c900f8212')