Add empty 'virtual' .ALL hierarchies as needed.

Add empty 'virtual' .ALL hierarchies as needed.

When using a --checkgroups file while tabulating,
valid but empty groups will be added with a posting
count of zero as needed. If all groups in a
sub-hierarchy are empty, the virtual '.ALL' group
for that sub-hierarchy was not created, though.

If local.test.dummy and local.test.binary were
both empty, both groups were added with a posting
count of '0', but local.test.ALL was not.

Now we loop through all hierarchy elements using
ParseHierarchies and add empty .ALL hierarchies as
needed.

Fixes #49.

Also fixing a typo in some comment. :-)

Signed-off-by: Thomas Hochstein <thh@inter.net>