* Update module_utils.six to latest
We've been held back on the version of six we could use on the module
side to 1.4.x because of python-2.4 compatibility. Now that our minimum
is Python-2.6, we can update to the latest version of six in
module_utils and get rid of the second copy in lib/ansible/compat.
* inventory: test 'all' & 'ungrouped' groups created by default
* Mention default groups 'all' & 'ungrouped'
* Update intro_inventory.rst
Minor grammatical edit.
There were no inventory-specific unit tests earlier, so we add a new
directory for them with some initial low-level tests of _split_pattern
with various valid and deprecated pattern strings.