Move slim port base calculation to one place.
Move slim port base calculation to one place.

amolenaar/fitnesse,jdufner/fitnesse,hansjoachim/fitnesse,rbevers/fitnesse,hansjoachim/fitnesse,jdufner/fitnesse,jdufner/fitnesse,rbevers/fitnesse,hansjoachim/fitnesse,amolenaar/fitnesse,amolenaar/fitnesse,rbevers/fitnesse