Conflicts:
	slapos/grid/SlapObject.py

create_tap is true by default.
rationale: better understanding of what does the option, and simpler use of
slapgrid.

Gets rid of the last class property in this file.

Your brain should pop out through your eyes already: this code is setting
a *class* property. On a class which is used as a base class everywhere in
this file. Mouhaha. *sob*

This code is called during upgrade and shall work without interactions.

This explains speed of migration, doing nothing usually takes not time.
Unfortunately this optimisation has to be dropped.

In Vifib configuration invoices are simple.

It just does not work [tm].