This is not a complete fix for the problem that Info doen't propigate
from the called property when code does something like:
hostname <- asks hostName
ensureProperty $ foo hostname
Instead, I just eliminated the need to implement hasPassword that way,
by making the PrivData Info use a HostContext which automatically
gets the right hostname passed to it.
All other uses of withPrivData don't have the problem. It's still possible
for the user to run into the problem if they write something like the
above, where foo is a property that uses privdata. However, all properties
that take a Context now also accept a HostContext, so it's at least less
likely the user needs to write that.