Before 442b86, this worked because we always unconditionally made tgt checked if
src was checked. With the new 3-way-diff algorithm for value and checkedness, we
need to save the checkedness of tgt before any DOM manipulation that could
uncheck it.
server's rendering has changed.
This fixes two independent issues:
- If the user has changed the value in a preserved field, and something causes
the field to be rerendered, and the re-rendering renders the same value that
was originally rendered, this now preserves the user's change rather than
reverting to the original value.
- INPUTs with type other than TEXT can now have reactive values (eg,
type=SUBMIT).
