Enhanced CTorrent Code

Fix unlikely but potential division by zero in Prefetch.

m_err_count should be int to handle reduction

Reduce peer error count on piece completion

Correct messages that should be Debug instead of Warning

HealthCheck improvement to reduce redundant receipts from high latency peers.

Improve choke oscillation detection to reduce duplicate (redundant) receipts.

Efficiency improvement in PendingQueue functions.

Detect a duplication inconsistency in Pending.

Duplicate request management:
Spread request duplication more evenly among outstanding pieces.
Limit duplicate requests for a piece to the number of outstanding slices.
Track the number of pieces requested as duplicates.
Track pieces for which slices have been requested or received from multiple peers.
Improve GetDownloads efficiency.

Accept cancelled data from a peer if still needed.