This seems redundant, since propellor must be running to ensure such a
Property, but a Property to install propellor is useful when eg, creating a
disk image that itself will need to run propellor. --[[Joey]]

Should support:

* Cloning the git repo propellor is running in. (Using eg `hostChroot`)
* Cloning some other git repo.
* Installing the precompiled propellor binary.
* Installing the propellor haskell library using cabal/stack/apt.

Much of this is already implemented, in non-Property form, in
Propellor.Bootstrap, but will need adjustments for this new context.
--[[Joey]]

> [[done]]
