This patch add doc about target attributes in the doc.

Thanks,
Hui


2012-08-29  Hui Zhu  <hui_zhu@mentor.com>
	    Stan Shebs  <stan@codesourcery.com>

	* agentexpr.texi (Bytecode Descriptions): Update "setv" and
	"getv".
	* gdb.texinfo (Maintenance Commands): Add
	"maint load-target-attributes" and "maint clear-target-attributes".
	(General Query Packets): Add "qXfer:target-attributes:read",
	"qTA" and "QTA".
	(Target Attributes): New appendix.