Add "monitor workgroup"

	* src/GdbServer.cpp (GdbServer::initProcesses): Assert thread
	addition worked.
	(GdbServer::rspCommand): Add "monitor workgroup" command and rejig
	logic slightly to accomodate.
	(GdbServer::rspCmdWorkgroup): Created.
	* src/GdbServer.h: Add rspCmdWorkgroup.
	(ProcessInfo::addThread): No error message, just return TRUE of
	FALSE to indicate success or not.
	(ProcessInfo::eraseThread): Created.
	* src/ProcessInfo.h: Add eraseThread, change prototype of addThread.