Import Debian changes 0.13.0-0.1

bitcoin (0.13.0-0.1) unstable; urgency=medium

  * Non-maintainer upload.
  * New upstream release.
  * Allow compilation with gcc/g++ 6. (Closes: Bug#835963)
  * Additional fixes for openssl 1.1 compatibility. (See Bug#828248)
  * Check if -latomic is needed (it is on mips*).
  * Remove reproducible build patch, since leveldb build system is
    no longer used in 0.13. (See Bug#791834)
  * Update description since the blockchain is much more than "several GB"
    now. (Closes: Bug#835809)