pcf8591read example ignores address parameter

[lurch]

quick2wire-python-api/examples/pcf8591read reads the optional first command line argument into a variable named 'address', but this variable isn't then used anywhere else!
The fix is to replace:
adc = PCF8591(i2c, FOUR_SINGLE_ENDED)
with:
adc = PCF8591(i2c, FOUR_SINGLE_ENDED, address)

I haven't checked to see if a similar bug affects any of the other examples.

Once this bug has been fixed, then http://quick2wire.com/testing-the-i2c-analogue-board-part-2/ (and its screenshot) will need to be updated to use ./pcf8591read 72 1 since 48 in hex is 72 in decimal.