bytes -> bytearrays in read procedures

[esel7353]

I had to transmit a lot of 128MB waveforms from my scope to the computer, which was extremely slow. After changing all the "bytes +=" parts in the read procedures to "bytearray.append", I was able to speed the process up by a factor of 10.

So I suggest applying these changes here too.

[sauerburger]

see github.com/sauerburger/pytohn-vxi11 for the updated version

[alexforencich]

Should be fixed now.