Mixed address (or 4-in-6) not parsed correctly

[bensonrodney]

When parsing a mixed (or 4-in-6) address the '6' part is stripped and only the IPv4 part is returned in the resulting integer.

Eg (using ipython):
In [1]: from ipcalc import IP

In [2]: x = IP("fd::0.0.0.1")

In [3]: x.ip
Out[3]: 1