Use alias wrapper only if it is really needed
Created by: racke
This is a follow up to #943 (closed). It is established security practice to only elevate privileges if really needed. Currently we always call the wrapper instead of the newaliases program, which is a bad idea.
Especially as the wrapper is usually not needed. With postfix you are usually running postmap. Exim can use plain text files, so it doesn't need any newaliases program.
So we could call the program directly (at least in the default configuration).
Does that make sense?