Allow start from lib

[yarkinwho]

Resolve #152

This PR supersede PR #182

[taokayan]

Looks good. i get the following behavior which is expected:

if native block LIB is x,
then evm node may get the native block number from the evm LIB block, which may result in x - 1. This is because of 2 native blocks map to 1 evm block.

verified account balance after couple times of shutdown-restarts, in which there're transfer transaction in each native block.