Change the definition of base-hash to be the mergebase of %home with the
OTA source. This means it's the most recent successfully-applied
update, which is usually the most important information.
Add sour-hash, which is the hash of the most recently *downloaded*
update, regardless of whether it applied successfuly (ie the old
base-hash).
Add a summary of the various hashes at the top of gen/trouble.
We need to get updates directly into %home in case the marks depend on
changes to hoon.hoon. %base has no reason to exist.
Our ota strategy is now to merge from parent/kids to home, then
parent/kids to kids.
