Function grin_chain::pipe::rewind_and_apply_fork

pub fn rewind_and_apply_fork(
    b: &Block, 
    ext: &mut Extension
) -> Result<(), Error>

Utility function to handle forks. From the forked block, jump backward to find to fork root. Rewind the txhashset to the root and apply all the forked blocks prior to the one being processed to set the txhashset in the expected state.