libproxy (http://libproxy.googlecode.com) is a library designed to abstract and simplify the process of determining what, if any, proxy settings a program should use in a given environment. Neon uses libproxy for such a purpose, but Subversion doesn't make use of it (see issue #3740). And even if it did, with Subversion 1.8, libsvn_ra_neon is going away, leaving us with libsvn_ra_serf/Serf, which has no libproxy functionality at all. Users have come to expect that programs honor the de facto standards for configuration proxy information on their system ("Internet Settings" on Windows, environment variables on Unix, etc.). libproxy does the heavy lifting for us -- Subversion just needs to employ it.