(#650) Allow symlinks for configuration directories

Previously, pointing a setting like 'confdir' at a symlink to a directory would
replace the symlink with a directory. This was because files created by
settings implicitly managed links, rather than following them. This behavior is
now changed so that file settings will follow links.

The behavior of these symlinks is the same as any other file resource. That is,
if the target of the symlink doesn't exist, Puppet will consider this an
error. Similarly, if the target of the symlink is a file, then the symlink
will still be replaced with a directory, rather than replacing its target.

Reviewed-By: Jacob Helwig <jacob@puppetlabs.com>
Reviewed-By: Dominic Maraglia <dominic@puppetlabs.com>