ArduinoISP, PIN_MISO keeps the PULL_UP enabled after finish

[deulis]

Using ArduinoISP, when programming is over the PIN_MISO remain with the PULL_UP enable. This can interfere with other SPI devices connected at the same time on the SPI bus (as it happened in my case).

My solution was to add:
pinMode(PIN_MISO, INPUT);
in the end_pmode() method.

I recommend to add this line in the official ArduinoISP sketch.