Reduce checks of blkindex blocks.

Only check the last 100 blocks on startup in LoadBlockIndex instead of
the last 2500 as before.
Add analyseutxo RPC call.

Add the new "analyseutxo" RPC call that looks through the whole UTXO set
and calculates some statistics.
Merge pull request #29 from domob1812/reduce-startup-checks

Reduce checks of blkindex blocks.
Merge pull request #30 from domob1812/analyse-utxo

Add analyseutxo RPC call.