The attached patch implements the core awareness, as discussed at:

	http://thread.gmane.org/gmane.comp.gdb.devel/27468/

The most current spec can be found at:

	http://article.gmane.org/gmane.comp.gdb.devel/27548

To summarize, with this patch, when debugging against gdbserver:

* The -list-thread-groups command will report the cores that each
process runs on (with or without --available)
* It's possible to pass several thread groups to -list-thread-groups
* The *stopped output includes core number

For native debugging on Linux, roughly the same is also possible.

This is mostly MI change, but includes some remote protocol tweaks,
and documentation. I'd appreciate review of those parts.

- Volodya