Add attr component

This is needed in order to compile libcap2 which is required by LXC.

component/attr/buildout.cfg

+[buildout]
+
+parts = attr
+
+[attr]
+recipe = hexagonit.recipe.cmmi
+url = http://download.savannah.gnu.org/releases/attr/attr-2.4.46.src.tar.gz
+md5sum = db557c17fdfa4f785333ecda08654010
+configure-options =
+    --enable-shared=yes
+    --enable-gettext=no
+make-targets = install install-lib install-dev