Update path_dwim() to return absolute path

If path_dwim() is provided a relative path to a file, it will now return an
absolute path of the playbook directory + the relative file path.
Merge pull request #1818 from sfromm/issue1815

Update path_dwim() to return absolute path
Allow using connection: on the task level

This is the name of the setting on the play level, and the options.
Should be consistent.
Allow infinite depth task includes
Make inventory variables available to vars_files
Check for non-accepted arguments combined with task includes

Throw an appropriate error for it.
Allow only_if/when_* on task includes and apply it on all tasks within
Added additional template variables

Added two additional template variables
* template_fullpath - absolute path to the template
* template_run_date - date that the template was rendered
Documented these additional variables in the module documentation