Enhanced CTorrent Code

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

cleaner CancelRequest and Pending use

Report peer initial completeness in verbose mode.

fix conditions for performing peer health check

Update peer error counting