MI and modifying register value

[Jan Vrany]

Hi, 

while investigating MI client issue when setting a register value
from debugger I realized two things: 

1) There's an MI command to set register value: -data-write-register-values
   This command is not documented and looking at the code, seems to be somewhat
   half-implemented - does not use <format> parameter its comment mentions and
   only works for frame 0 (but using --frame 1 does not result in an error,
   it just silently changes value in frame 0). 

   Is this command some leftover that should not be used (but kept for some
   old clients)? Or is it something to fix? 

2) Another way to change register value is CLI command `set r4 = 0x4`. There's
   no mechanism the MI client gets notified about the change - there's no =register-changed
   async event. 

   Is this by purpose? I'd expect some kind of notification, just like there's =memory-changed
   event. Also, in Python API, there's memory_ckanged event which get triggered when
   using `set` to modify register. 

Best, Jan