Do not inv old or missing blocks when pruning
Do not inv old or missing blocks when pruning

When responding to a getblocks message, only return inv's as
long as we HAVE_DATA for blocks in the chain, and only for blocks
that we aren't likely to delete in the near future.

syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin