TypeError when using MCP4921 or MCP4922

[GoogleCodeExporter]

WebIOPi version used?
=> 0.7.1

Python version used?
=> 3.2

Raspberry Pi board revision? (1 or 2)
=> 2

Issue #48 added a new vref parameter to the 
webiopi.devices.analog.mcp492X.MCP492X class but the 2 subclasses for MCP4921 
and MCP4922 were not correctly updated to reflect this.

As a result trying to use either results in:

Traceback (most recent call last):
  File "/usr/local/lib/python3.2/dist-packages/WebIOPi-0.7.1-py3.2-linux-armv7l.egg/webiopi/__main__.py", line 75, in <module>
    main(sys.argv)
  File "/usr/local/lib/python3.2/dist-packages/WebIOPi-0.7.1-py3.2-linux-armv7l.egg/webiopi/__main__.py", line 69, in main
    server = Server(port=port, configfile=configfile, scriptfile=scriptfile)
  File "/usr/local/lib/python3.2/dist-packages/WebIOPi-0.7.1-py3.2-linux-armv7l.egg/webiopi/server/__init__.py", line 66, in __init__
    manager.addDevice(name, driver, args)
  File "/usr/local/lib/python3.2/dist-packages/WebIOPi-0.7.1-py3.2-linux-armv7l.egg/webiopi/devices/manager.py", line 28, in addDevice
    dev = devClass()
  File "/usr/local/lib/python3.2/dist-packages/WebIOPi-0.7.1-py3.2-linux-armv7l.egg/webiopi/devices/analog/mcp492X.py", line 52, in __init__
    MCP492X.__init__(self, chip, 2)
TypeError: __init__() takes exactly 4 arguments (3 given)

The fix is simple; pass on the `vref` parameter to the base class:

class MCP4921(MCP492X):
    def __init__(self, chip=0, vref=3.3):
        MCP492X.__init__(self, chip, 1, vref)

class MCP4922(MCP492X):
    def __init__(self, chip=0, vref=3.3):
        MCP492X.__init__(self, chip, 2, vref)

Original issue reported on code.google.com by zopati...@gmail.com on 1 Aug 2015 at 12:51