Implemented array subscript lookup in JSON::Object::find.

Review: https://reviews.apache.org/r/26634
Fixes necessary due to JSON::Array::values change to std::vector.

Review: https://reviews.apache.org/r/26635
Mark running tasks killed during framework shutdown.

When a framework is shut down e.g. by calling driver.stop() from the
scheduler, running tasks are marked KILLED before migrating them to
completed.

Review: https://reviews.apache.org/r/25250
Fixed a spelling mistake.
Introduced a FutureResult action.

The FutureResult action enables capturing the result from an inner
action, e.g., an Invoke* action.

Review: https://reviews.apache.org/r/27199
PortMappingIsolator: Swap TX/RX in statistic collection in usage

statistics collected on the host end of veth pair have reversed RX/TX of those in the container.

Review: https://reviews.apache.org/r/27154
Added a check in routing library due to a bug in libnl.

Review: https://reviews.apache.org/r/27105
Added documentation for egress rate limit control.

Review: https://reviews.apache.org/r/26423
Reordered functions in type_utils and added an equal comparator for
Volume.

Review: https://reviews.apache.org/r/27150
Adds Wizcorp to PoweredByMesos page.
Added Java replicated log implementation of State.

Review: https://reviews.apache.org/r/24341
Added functionality to create SVN based diffs of arbitrary strings.

Review: https://reviews.apache.org/r/24535
Added DIFF to the replicated log state storage implementation.

Review: https://reviews.apache.org/r/24536
Ensured post-reviews.py added newline between subject and body.
Updated svn::diff/patch to use newer versions of functions.
Added --with-apr and --with-svn to libprocess configure.
Added --with-apr and --with-svn to Mesos configure.
Fixed line wrap in state/log.cpp.
Adds Localsensor to PoweredByMesos documentation.
Pass executor directory to Isolator::prepare().

Review: https://reviews.apache.org/r/24177