Apache Serf

The serf library is a high performance C-based HTTP client library built
upon the Apache Portable Runtime (APR) library. It is permissively
licensed under the Apache License, v2.

Key features:

    multiplexed, asynchronous connections
    SSL/TLS support
    full HTTP pipelining
    multiple authentication modes (Basic, Digest, Kerberos/NTLM)
    zero-copy support for increased throughput

Serf is the default client library of Apache Subversion and Apache
OpenOffice

Requires SCons build system (available from PyPi)
but this specific package requires python2, because
the SContruct file (which is SCons' Makefile in python
language) uses python2 syntax.

SCons strictly doesn't require build_in_sourcedir (scons -Y), but
I don't see the point of separate sources anyway, when we start
each build from scratch.

I recommend to run this bee file with

    unshare -U -r ./serf.be0

instead of

    sudo ./serf.be0

Well, I think that is better for ANY bee file, but here we
invoke a downloaded PyPi package.

Our current subversion install doesn't work at all:

    buczek@sigusr2:/scratch/local$  svn co https://svn.resourcespace.com/svn/rs/trunk/
    svn: E170000: Unrecognized URL scheme for 'https://svn.resourcespace.com/svn/rs/trunk'
    buczek@sigusr2:/scratch/local$  svn co http://svn.resourcespace.com/svn/rs/trunk/
    svn: E170000: Unrecognized URL scheme for 'http://svn.resourcespace.com/svn/rs/trunk'

because subversion won't build with a client library for remote
repositories. Add configuration for Apache Serf.