fix for concat error

This fixes a - in my opinion - critical bug which leads to a puppet run abort.

using a fairly new concat and postgresql module, this happens:
* postgresql is the first module which uses concat which gets realized by puppet
* concat was not yet initialized, so it does its initialization (create `/var/lib/puppet/concat` ...)
* puppet aborts with a `user postgres not found` error

What happens is that on first run, without being initialized, the concat module wants to create its helper directories. But postgresql defines a standard user for all File{} objects, which does not yet exist (the package is not yet installed), and would be horribly wrong anyway.

I did not find any practical use of the general File{} definition, so I removed it, and so far it works.