Remove transactions from orphan pool.

[dajohi]

This change removes transactions in a newly connected block
from the orphan pool if they exist. This helps keep memory
usage lower.

[dajohi]

Another bonus with this fix, when the txs are removed from the orphan pool, orphans that are no longer orphans are moved to mempool and inv'd to peers.

[davecgh]

This logically reads well, but I want to manually test it before merging.

[davecgh]

While I know Go doesn't care about the function order, I'd prefer the unexported version comes before the exported version which depends on it. This is more consistent with the rest of the code.

[davecgh]

After reviewing this and thinking about it some more, I think a better approach to do this is to modify the removeTransaction function to also operate on the orphan pool. This would have the benefit of ensuring that any transactions which are also recursively removed also remove any orphans that depend on them. It also would only be a change in a single existing function instead of having to also modify the block manager, and will catch any other future cases of transaction removal.

I also noticed that, unlike normal transactions, orphans that now contain double spends due to newly connected transactions aren't currently removed either which this pull request doesn't address.

[davecgh]

I'm going to go ahead and merge this and open another issue to address the remaining cases. While this doesn't catch all of the cases, it is an improvement over the current code, works properly, and will allow the release to proceed.

[davecgh]

This has been rebased and merged as commit 4ad8622.