Fixed incorrect include of "common" headers in mesos-execute.

Review: https://reviews.apache.org/r/18667
Updated dash in front of flags for tar command in fetcher.

Review: https://reviews.apache.org/r/18697/
Changed SIGTERM to SIGKILL in command executor.

Reverting signal from SIGTERM to SIGKILL again per discussion in
https://reviews.apache.org/r/18604/.

Review: https://reviews.apache.org/r/18661
Changed Result::get to return a const reference.

Review: https://reviews.apache.org/r/18434
Added stout/interval.hpp to model boost interval set.

Review: https://reviews.apache.org/r/18093
Updated Makefile.am for the new interval set tests.

Review: https://reviews.apache.org/r/18333
Added a verify-reviews.py script that can run via CI to verify
Review Board reviews.

Review: https://reviews.apache.org/r/18676/
Added PicoJSON.

Review: https://reviews.apache.org/r/18699
JSON parsing and equality.

Review: https://reviews.apache.org/r/18700
JSON to protobuf parsing.

Review: https://reviews.apache.org/r/18701
Added a 'bool' to the test protobuf message.

Review: https://reviews.apache.org/r/18724
Include picojson when building libprocess.

Review: https://reviews.apache.org/r/18702
Include picojson when building Mesos.

Review: https://reviews.apache.org/r/18703
Made visitors be top-level structs.

When compiling with GCC 4.2 we need to keep Boost visitors as
top-level classes instead of nest them in functions.
Changed Future::get to return a const reference.

Review: https://reviews.apache.org/r/18443
Updates to mesos for Future::get() returning a const reference.

Review: https://reviews.apache.org/r/18445
Added a Sequence abstraction.

Review: https://reviews.apache.org/r/17476
Included std::tuple or boost::tuples::tuple within a tuples namespace of stout.

Namespace pull-in of std::tuple or boost::tuples::tuple, depending on
the availability of C+11. The results are part of a tuples namespace
of stout.

Example usage including fully qualified namespaces:

tuples::make_tuple(42, true); int foo = tuples::get<0>(tuple);

Review: https://reviews.apache.org/r/18360
Introduced ABORT as alternative to fatal.

Review: https://reviews.apache.org/r/18549
Removed define for gtests to use its own tr1 tuple.

gtest's tr1::tuple conficts with std::tr1::tuple for gcc-4.4. However,
we use tuple throughout mesos so we assume tr1::tuple or tuple is
available. As such, we don't need gtest to define one.

Review: https://reviews.apache.org/r/18722