BIP8: replace FAILING with MUST_SIGNAL

This removes the FAILING state and adds compulsory signalling during a
new MUST_SIGNAL phase during the last retarget period prior to the
timeout height.

This ensures that if a deployment occurs using bip8 with
lockinontimeout=false and timeoutheight=N, that a later deployment using
bip8 with lockinontimeout=true and timeoutheight=K, where K<N that any
chain where LOCKED_IN is reached prior to height K, will be accepted as
valid by nodes using either set of deployment parameters.

It also ensures that the soft-fork's changed rules are only enforced
on chain a retarget period after signalling indicates enforcement is
expected (which was not previously the case if the FAILING to ACTIVE
transition took place).

1 files changed, 0 insertions, 0 deletions

diff --git a/bip-0008/states.png b/bip-0008/states.png
index b6d73b7..6477ed3 100644
--- a/bip-0008/states.png
+++ b/bip-0008/states.png