Hang sending large payloads to Keysight scopes

[bobmcnamara]

On Mac OS X, sending data larger than ~128K to a Keysight scope results in a timeout in recvfrag. This is caused by a bug in sendfrag where the code should have used sock.sendall instead of sock.send:

def sendfrag(sock, last, frag):
    x = len(frag)
    if last: x = x | 0x80000000
    header = struct.pack(">I", x)
    sock.sendall(header + frag)

[alexforencich]

Good find with sendall, this will be fixed in the next release.