PWR toggle does not restart program when USB connected

[AndyLindsay]

On other platforms, switching PWR from 1 to 0 to 1 again restarts the program regardless of whether the device is connected to the USB port. Con be observed on Rev A5 and Rev A boards up to firmware/library v0.3.4.

1. Set PWR to 1
2. Use parallax.py library from 0.3.4 branch's library folder if you are using a Rev A board or from the master branch's library folder if you are using the rev A4 board.
3. Run Test_Piezo_Beep_Then_Loop.py
4. Leave USB connected
5. Set PWR to 0
6. Setting PWR back to 1 does not restart the program; micro:bit reset is required.
7. This can be repeated with Test_Piezo_Beep_Then_Loop.py. Although some items behave differently with loop vs. non loop programs, this does not.

# Test_Piezo_Beep.py

from parallax import *

bot(22).frequency_out(300, 2000)

# Test_Piezo_Beep_Then_Loop.py

from parallax import *

bot(22).frequency_out(300, 2000)

while True:
    bot(21).digital_write(1)
    bot(21).digital_write(0)

[AndyLindsay]

Addressed in cyberbot-0.3.7. See branch and zipped code.