Spack Infrastructure

Need to undo the below and retest at least spack spec for icaruscode and cosmosis, possibly with ~libxml2 in packages.yaml for python:

diff --git a/var/spack/repos/builtin/packages/gettext/package.py b/var/spack/repos/builtin/packages/gettext/package.py
index 8eb0ad6..24b0516 100644
--- a/var/spack/repos/builtin/packages/gettext/package.py
+++ b/var/spack/repos/builtin/packages/gettext/package.py
@@ -29,7 +29,7 @@ class Gettext(AutotoolsPackage, GNUMirrorPackage):

     # Recommended dependencies
     depends_on('ncurses',  when='+curses')
-    depends_on('libxml2',  when='+libxml2')
+    # depends_on('libxml2',  when='+libxml2') # cycle avoidance mengel@fnal.gov
     # Java runtime and compiler (e.g. GNU gcj or kaffe)
     # C# runtime and compiler (e.g. pnet or mono)
     depends_on('tar',      when='+tar')
-- a/var/spack/repos/builtin/packages/libxml2/package.py
+++ b/var/spack/repos/builtin/packages/libxml2/package.py
@@ -28,7 +28,8 @@ class Libxml2(AutotoolsPackage):
     depends_on('xz')

     # avoid cycle dependency for concretizer
-    depends_on('python+shared~libxml2', when='+python')
+    #depends_on('python+shared~libxml2', when='+python')
+    depends_on('python+shared', when='+python')
     extends('python', when='+python',
             ignore=r'(bin.*$)|(include.*$)|(share.*$)|(lib/libxml2.*$)|'
             '(lib/xml2.*$)|(lib/cmake.*$)')

--- a/var/spack/repos/builtin/packages/python/package.py
+++ b/var/spack/repos/builtin/packages/python/package.py
@@ -71,7 +71,7 @@ class Python(AutotoolsPackage):
     extendable = True

     # Variants to avoid cyclical dependencies for concretizer
-    variant('libxml2', default=True,
+    variant('libxml2', default=False,
             description='Use a gettext library build with libxml2')

     variant(