In read_usb(), don't print or memcpy the contents of the receive
buffer if the read failed.  Also, check lengths and print warnings if
they are inconsistent.
Read and discard the response to the final FF command.  Otherwise it
can remain buffered on the EC3 and be unexpectedly returned to the
next program that attempts to use the EC3.  With this change,
"ec2device --port USB" finally works reliably on NetBSD through
an EHCI and a hub.
Merge branch 'master' of github.com:gson1703/ec2-newer

Conflicts:
	src/ec2drv/ec2drv.c