misc.cc, misc.h: (xhuman) new function.
	* Job.cc, Job.h: (GetTransferRate) new method;
	  (GetBytesCount) count recursively over descendants.
	* CopyJob.cc, CopyJob.h, FileCopy.h: (GetTransferRate) implement;
	  (GetTimeSpent) don't count overlapped time intervals twice;
	  (GetBytesCount) count recursively for real time monitoring.
	* MirrorJob.cc, MirrorJob.h: show real-time bytes transferred and
	  rate in the mirror job title.