This binds the virDomainGetBlockInfo API to python's blockInfo
method on the domain object

>>> c = libvirt.openReadOnly('qemu:///session')
>>> d = c.lookupByName('demo')
>>> f = d.blockInfo("/dev/loop0", 0)
>>> print f
[1048576000L, 104857600L, 104857600L]

* python/libvirt-override-api.xml: Define override signature
* python/generator.py: Skip C impl generator for virDomainGetBlockInfo
* python/libvirt-override.c: Manual impl of virDomainGetBlockInfo