Pre- & Postconditions
For the first operation (adds a new output device to the
spooler together with its associated print limit):
Precondition:  the output device name does not already
exist and that there are currently less than MaxDevs
output devices known to the spooler
Postcondition: the name of the new device is added to the
collection of existing device names, a new entry is formed
for the device with no files being associated with its
queue, and the device is associated with its print limit.