consensus fields (since the untrusted db might not have the data we
need when verifying). Also, when calculating consensus quirks, check if
a name operation is the first NAME_IMPORT for a name in order to handle
the NAME_IMPORT fee quirk correctly.
* identify and preserve invariant properties that must hold across name
state-transitions (like no-collisions, or limiting fields that can
change).
* add history validation
* identify consensus-bearing fields, and how each state-creation or
state-transition may affect them (and add runtime checks to see that
they only affect the fields we say they will)
* add decorators that we can apply to name operations to enforce the
above.
