Added an endpoint for retrieving the registry.

Review: https://reviews.apache.org/r/19657
Added support to assign all threads of a process to a cgroup.

Review: https://reviews.apache.org/r/19699
Added support to look up thread ids using /proc on Linux.

Review: https://reviews.apache.org/r/19361
Changed cgroup verification to accept an empty cgroup to permit specifying the
root cgroup.

Review: https://reviews.apache.org/r/19700
Added support to move the slave into separate cgroup for monitoring.

Review: https://reviews.apache.org/r/19248
Updated cpplint.py to analyze hpp files.

Updated cpplint.py from
https://google-styleguide.googlecode.com/svn/trunk/cpplint/cpplint.py
and added hpp files as valid extensions.

Review: https://reviews.apache.org/r/19060
Minor fix for local.cpp to not set "slave_subsystems" flag.
Set the executable bit on mesos-style.py.
Add explicit to single argument constructors in libprocess.

Applied either "explicit" or "/*implicit*/" to all single-arg
constructors in lib process that do not take the constructed type as
parameter.

Sorted out which denotation to choose by compiling mess and fixing all
the compile errors and by estimating whether implicit conversions might
be intended by the original authors.

Review: https://reviews.apache.org/r/19086
Fixed tabs in stout.

Review: https://reviews.apache.org/r/19738
Fixed tabs in libprocess.

Review: https://reviews.apache.org/r/19739
Fixed tabs in mesos.

Review: https://reviews.apache.org/r/19740
Added style checker to verify-reviews.py.

Review: https://reviews.apache.org/r/19741
Changed active_rules in mesos-syle.py to array for easier management.

Review: https://reviews.apache.org/r/19743
Cleaned up a continuation in launcher.cpp.

Review: https://reviews.apache.org/r/19701
Updated RemoveSlave to use RepeatedPtrField::DeleteSubrange().

Review: https://reviews.apache.org/r/19712
Added a const qualifier to Stopwatch::elapsed.

Review: https://reviews.apache.org/r/19760
Fixed mesos-<start|stop>-cluster.sh to not report success on failure.

This is a small enhancement to mesos-<start|stop>-cluster.sh, so it
won't say kind of *OK* if it did fail.

Review: https://reviews.apache.org/r/19173
Fixed a compiler warning using UNREACHABLE in zookeeper.cpp.

Review: https://reviews.apache.org/r/19719
Enhanced DRF by including past allocations.

The DRF allocator (master/drf_sorter.hpp|cpp) currently only uses a
framework's share to determine an ordering for allocating
resources. When there are very few resources to go around it's
possible that a framework will get allocated resources (making it have
a dominant share larger than others), use those resources, then return
those resources (making it's dominant share equal to the share of
others), and then get reallocated the resources _again_ because its
dominant share is equal to others. This can cause starvation for
frameworks.

Review: https://reviews.apache.org/r/19090