Add support for parsing R-XML URL versions. (#2525)

* Add support for parsing R-XML URL versions.

* Better url-parse debug output.

- just print the debug stuff all the time.

* fix R-XML versions.

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

@@ -34,7 +34,8 @@ class RXml(Package):
     url      = "https://cran.r-project.org/src/contrib/XML_3.98-1.4.tar.gz"
     list_url = "https://cran.r-project.org/src/contrib/Archive/XML"
 
-    version('3.98-1', '1a7f3ce6f264eeb109bfa57bedb26c14')
+    version('3.98-1.5', 'd1cfcd56f7aec96a84ffca91aea507ee')
+    version('3.98-1.4', '1a7f3ce6f264eeb109bfa57bedb26c14')
 
     extends('R')