]link.create targetns single-file should load into, not overwrite targetns

[mkromberg]

]link.create ⎕SE.CITA HttpCommand should create ⎕SE.CITA.HttpCommand.

[mkromberg]

This is not generally possible, although it looks sensible in the case where the source is an existing file, it is not symmetrical. What if HttpCommand is not found, should this export all of ⎕SE.CITA? I could imagine allowing a trailing dot in the namespace name:

]Link.Create ⎕SE.CITA. HttpCommand

... to imply -source=dir and mean "use whatever name the file defines as the target", but given the current workload I am pushing this to the Link 5.0 milestone.