Instead of maintaining not-easily-tested instructions for building BerkeleyDB
in doc/build-unix.md, package the installation as a script in contrib/. This
allows shared usage from a number of contexts, e.g. Docker.
Thanks to @jonasschnelli, @laanwj for feedback.
- Python 3 now supported.
- Bump boost version to 1.61 - one boost patch no longer needed.
- All checked with OpenBSD 5.9, except for the clang part, I left this
as-is for someone adventurous.
- Mention overriding resource limits, OpenBSD's default ulimit does not
suffice for building Bitcoin Core with gcc 4.9.3.
Jianping Wu