Log Message:
Update to 0.15.  Closes PR 38144.  Changes:
btpd 0.15:
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Bug fixes:
- The event loop could busy loop for up to a millisecond sometimes.
- On some platforms btpd couldn't initiate connections to other peers.
- The timer code was broken on MacOS X.

btpd 0.14:
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Misc:
- IPv6 support.
- Bans peers with bad data.
- Better tracker compatability and more reliable tracker communication.
- Show tracker counts in btcli stat.
- Compiles on Solaris 10.
- Btpd will now signal startup failures via the process exit value and
  print the failure reason to stdout.
- Better shutdown and torrent stop behaviour.
- Needs pthreads again.
- Removed libevent in favour of own event loop code.

Bug fixes:
- An integer array was misaligned, which could cause crashes on systems
  with alignment requirements. E.g., on XScale arm.
- An error in the torrent parsing code could cause crashes.
- The '--topdir' option to btcli add didn't work properly for single file
  torrents.
- The system name lookup scheme is now used. In btpd 0.13 only dns lookups
  were performed.

btpd 0.13:
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Misc:
- cURL is no longer required. btpd now uses its own http client.
- btpd doesn't use threads anymore, so pthreads are not required.
- Needed parts of libevent are now included in btpd.
- I/O errors for torrents no longer make btpd shut down. Instead the
  problematic torrent is stopped.
- Added the option '--ip' to specify the ip address btpd will report
  to trackers.
- Resume file format changed. Already added torrents will be retested once.
- The torrent info (ratio etc.) are now saved regularly.
- Reduced the amount of outgoing data kept in memory.