Enhanced CTorrent Code

When reading a piece for hash check, avoid expiring parts of the same piece from the cache.

Use staged data gaps to influence download piece selection.

Extra staging file list entry could be created due to max size.
Skip merging if staged data is already present in the target file.

Console is unresponsive when downloading slowly (IsIdle problem).

Console is unresponsive when downloading slowly (IsIdle problem).

When download is complete, queue pieces to flush instead of flushing everything immediately.

Correction in cache aging of a piece.

When flushing a cache entry, always flush all entries for the same piece.

Cache management bug due to expiration during I/O

Cache management bug due to expiration during I/O