Revised QVSS mouse support from Matt Burke to address #60

This is definately much better, but I observed some strange behaviors in my initial testing when the mouse reached the window edge.
QVSS: Fix to handle when cursor is near the right edge of the screen and only partially visible.

Prior fix for cursor tracking allowed this to now be observed.

The description of the prior change should have been:

The status bits need to be set in the upper byte of the DUART receiver buffer. This is not mentioned in the DEC manual but I found a Phillips datasheet for the 2681 chip, which has a small footnote about it.
VAX: Added Register Bit Field definitions for the PSL register
VAX630: Added register bit fields for the watch device and read/write tracing for watch register activity.
VAX630: Added register bitfields for the IPC (Doorbell) register and read/write tracing.
VAX630: NVR corrected to be 64 bytes instead of 128. Added NVR read/write debug tracing.

   - Fixed broken NVR Examine/Deposit
   - Added SHOW CPU LEDS
VAX630: Fix watch chip behavior the first time a file is attached to the NVR device.
sim_debug: Fixed to produce output when the format string is a bare newline character.

Fixed bitfield output to properly present the prefix when appropriate.

This closes issue #62
Clear storage and branch preserves B register (Van Snyder)
Merge Fixes from Bob Supnik's updates
SCP: Fix Set Command dispatching and HELP dev SET output

 - Fixed set MTAB dispatching to not dispatch to unit specific routines when only a device is specified in the command
 - Fixed HELP dev SET output to avoid displaying SET commands which aren't valid for SHOW only cases