There will be a way to retrieve the list of all system installations,
not just the default one, so we rename this for backward compatibility.
Note that some (most?) of the places where we will be now using this
renamed function will likely have to migrate to using specific system
installations, but we don't have the necessary APIs yet so we do this
as an initial step to all the incremental changes that will come next.
The commands: install, update, uninstall, info, make-current and run
now supports specifying a partial ref for the name. This is a different
way of specifying optional arch and branch arguments.
For instance org.app.App//master is the same as "org.app.App master" or
"--branch=master org.app.App".
This is useful if you're cutting and pasting from e.g. the list -d output.