* Drop bradfitz/iter dependency
`range iter.N` looks nice and doesn't allocate, but unfortunately using a `range` expression blocks a function from being inlined wherever it's used (for now). It's not that we need inlining in all cases, but I do think a C-style for loop looks just as nice and is probably clearer to the majority. There also aren't any clear disadvantages to changing (unless you just happen to dislike the look of C)
* Update misc_test.go
* Update rlreader_test.go
* Update torrent_test.go
* Update bench_test.go
* Update client_test.go
* Update iplist_test.go
* Update mse_test.go
* Update peerconn_test.go
* Update peerconn.go
* Update order_test.go
* Update decoder_test.go
* Update main.go
* Update bench-piece-mark-complete.go
* Update main.go
* Update torrent.go
* Update iplist_test.go
* Update main.go
This might help break the situation where anacrolix/torrent Clients that are connected to each other never release a connection until there's new connections that look more promising.
Pieces could get queued for hash multiple times when we receive chunks if the piece starts getting hashed before we're done writing all the chunks out. This was only found because piece hashing currently only checks the incomplete data, which is missing after the first piece hash passes, the data is marked complete, then the subsequently queued hash has nothing to read.
This prevents too many pending writes building up. Webseed peers re-request synchronously, and the writes are done asynchronously, so they download too quickly and there was no backpressure. The backpressure now is provided by the upper limit on outstanding requests per connection.
New requests weren't being issued to the current peer when being deleted. For webseeds, this would cause them to not bother issuing new requests indefinitely.
(cherry picked from commit 146a16df4ea26d33b0ce0391c8220de14c9e18f4)
