[Simh] Tiny bit of progress on RSTS/E RK07 issue

[Bob Supnik]

It looks like there are multiple problems.

The first was that the drive type was being misidentified during system 
startup (in the routine RMLOOK in INIONE.MAC). This was due to a problem 
in update_hkds, which incorrectly cleared the error register (HKER[drv]) 
if the drive wasn't attached. In fact, all sorts of errors can be 
generated by a dismounted drive, including, most critically, drive type 
error. Without this, the drive is misidentified as an RK06.

However, the INIT command still fails with "drive hung", and drive type 
mismatch errors are occurring. Now I need to trace the driver itself to 
see why it is trying commands to an identified RK07 with an RK06 drive type.

Standalone INIT can initialize an RK07, but then MOUNT fails, so an 
interaction problem remains between the driver and the simulator.

/Bob Supnik