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-plyr/package.py

@@ -36,6 +36,7 @@ class RPlyr(RPackage):
 
     homepage = "http://had.co.nz/plyr"
     url      = "https://cran.r-project.org/src/contrib/plyr_1.8.4.tar.gz"
+    list_url = "https://cran.r-project.org/src/contrib/Archive/plyr"
 
     version('1.8.4', 'ef455cf7fc06e34837692156b7b2587b')