Preserve relative paths in Link resource

* Fixes https://github.com/opscode/chef/issues/2580.
* Reverts https://github.com/opscode/chef/issues/1901. (Except the new test)
* Replaces https://github.com/opscode/chef/pull/2615.

I'm much more happier with this change :smile: 

/cc: @randomcamel / @lamont-granquist / @jdmundrawala