Added a configure time check for building a native python egg.

This autoconf check does a rather complex test for covering MESOS-799.

It builds and test-runs a minimal egg that links against a static
library that imports a standard C++ library object. A static library
(built using the standard mesos build settings) is needed in this
puzzle because the egg producing distutils possibly use slightly
different build settings (derived from python-config).

If this check succeeds, we can be rather sure that the mesos-egg
itself will be functional from a build-env point of view.

From: TILL TOENSHOFF <toenshoff@me.com>
Review: https://reviews.apache.org/r/16436
Fixed namespace resolution in slave/paths.hpp.

From: Ian Downes <ian.downes@gmail.com>
Review: https://reviews.apache.org/r/16788