Added file failure tests.

These check that file blocks fail when underspecified.
Expanded directory block tests

These ensure that directories fail when underspecified, and fix
directory group behavior (revealed by tests).
Includes some extra testing for directory_block coverage and minor fixes
to directory_block code.
Added nose-cov to test requirements, for automated builds.
Improved coverage of file_block and block.identifier
Added testing for manifest action expansion and completed action coverage.
Completed coverage of tokenizer.
Removed unused logic from conf application.

Manifest expansion handles recursive configuration application, so
having configuration application handle that as well is redundant.
Merge branch 'refactor/test-coverage' into dev