Following discussion, this patch adds feature capability handling
(enable, disable, and automatic "qSupported" query) for the reverse
execution packets "bs" (backward step) and "bc" (backward continue
in the gdb remote protocol.

Cc:ing Jakob and Greg, whose remote targets may be affected.
What you guys will want to do is have your remote targets
recognize the "qSupported" query from gdb, and respond with:

	ReverseContinue+;ReverseStep+

This will tell gdb that your targets support those two commands.

Otherwise, they default to "disabled", and a user would need
to enable them with these commands (which might be added to a
.gdbinit file):

	set remote reverse-continue on
	set remote reverse-step on

Pedro, does this look like what you expected?

Michael