Allow for the xinclude file to not be found

Including adding tests for that case
Replace items() with iteritems() in various places

to reduce memory usage
Merge branch 'remove_viewitems' into aptivate

* remove_viewitems:
  Replace items() with iteritems() in various places
Merge branch 'xinclude' into aptivate

* xinclude:
  Allow for the xinclude file to not be found