GDB-Protocol: Script command

[Andrew Cagney]

When debugging both embedded targets and simulators there is often the
need to pass across target specific commands.  As an example, GDB, when
talking to a builtin simulator, allows `sim' commands:

	(gdb) target sim
	Connected to simulator
	(gdb) load
	....
	(gdb) sim trace instruction on
	(gdb) run
	0x12432: ld r1, r2
	...

There is no corresponding mechanism available in the remote protocol. 
I'd like to propose that the ``qS'' prefix be reserved for this:

	<- qS<some-command>
	-> output-from-command

(Well another posibility would be ``QScript=<command>''.)  Potential
issues include:

	o	encoding of special charcters
		(should we just pass hex?).

	o	security

	o	the corresponding GDB command
		(I've no idea, suggestions welcome).


	Andrew