Blockindex compatibility fix, startup speedup

[instagibbs]

We diverged from the 0.14 codebase, fix included here as well as performance speedup on initial load.

In 0.14 we did no signature checking at all, but the signature checks were what alerted me to the incompatibility, so I opted to preserve some of that as sanity check.

[instagibbs]

Output from updated instance(14->master) for reference:

gettxoutsetinfo
{
  "height": 234901,
  "bestblock": "eb90f88eee9e0c28998e91c3f341d9ff8f191d8e753b7608b96a242f173d9ba2",
  "transactions": 29614,
  "txouts": 31364,
  "bogosize": 2352300,
  "hash_serialized_2": "2c56d2de39ed8a8e4baee8ba0b28ccdcd42a5a61586f7ada43a4e48d7c8ea24f",
  "disk_size": 3432870,
  "total_amount": 9770549.77818588
}

[instagibbs]

On freshly synced elements master: invalidateblock ebf01047f8ca052c858cf6a43f111242a133f4aeb5cefed5d1952683816c0a1d which is height 234902:

gettxoutsetinfo
{
  "height": 234901,
  "bestblock": "eb90f88eee9e0c28998e91c3f341d9ff8f191d8e753b7608b96a242f173d9ba2",
  "transactions": 29614,
  "txouts": 31364,
  "bogosize": 2352300,
  "hash_serialized_2": "2c56d2de39ed8a8e4baee8ba0b28ccdcd42a5a61586f7ada43a4e48d7c8ea24f",
  "disk_size": 3390414,
  "total_amount": 9770549.77818588
}

Now syncing using liquid public release and will post results when finished.

[instagibbs]

liquid public release sync:

gettxoutsetinfo
{
  "height": 234901,
  "bestblock": "eb90f88eee9e0c28998e91c3f341d9ff8f191d8e753b7608b96a242f173d9ba2",
  "transactions": 29614,
  "txouts": 31364,
  "bytes_serialized": 3073917,
  "hash_serialized": "44f47d09a7f957e44df0f0cc352907d849de1fa400d218d41c33fccb59dc2e51"
}

[stevenroose]

tACK 0baa135

Converted my old liquidd in a flash :)