Enhanced CTorrent Code

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.

Reduce duplicate data receipt:
Avoid duplication to high-latency/slow peers.
When duplicating or reassigning requests, move immediate incoming slices to the end of the queue.

Improve randomness of CopyShuffle

Improve data counting and reporting.
If hash check fails, don't re-request the same piece from that peer.

Improve piece request reassignment:
Reassign only if proposer's queue is empty.
Consider any piece in the slower peer's queue.
Improve download rate comparison method.
Allow reassignment in endgame mode.

report system error message when file creation fails