Prametrize !includedir

Hardcoded path provided by puppet is now replaced by providing only the final directory as on
most systems includedir is provided by package and it's matter of user to provide it if he
wants to override it. This also allows disabling including at all.

(cherry picked from commit 26204437ef852951d4f998298867855b6eb1488d)

Conflicts:
	manifests/params.pp
In puppet `''` is actually a false value, so you can just say `if $includedir {`