Search the Openlist for the device named in Devnam.
If not found, trap execution. Otherwise, perform the following
operations:
Set $IO to the device named in Devnam, and make this device
the current device for all input and output.
If Result contains any device parameters, find the device
named in Devnam in the Devicelist, and change those parameters
which appear in Result to their new value from Result.
Perform any initialization procedures for the device named in
Devnam according to its device parameters in Devicelist.
Devnam.