Added process::await() for asynchronously awaiting for Futures to
transition from pending.

Review: https://reviews.apache.org/r/13381
Fixed session handling on OS X.

On OS X, it appears that getsid() returns ESRCH for zombie processes.

Review: https://reviews.apache.org/r/13396
Rewrote os::read(string path) to use getline.

The existing implemenation does not work well when used to read
files in the /proc pseudo filesystem.

From: Jiang Yan Xu <yan@jxu.me>
Review: https://reviews.apache.org/r/13387
Changed proc::status(pid) to use os::read().

This was changed because ifstream threw unexpected exceptions.

From: Jiang Yan Xu <yan@jxu.me>
Review: https://reviews.apache.org/r/13388
Improved the ReaperTest by using os::Fork.

From: Jiang Yan Xu <yan@jxu.me>
Review: https://reviews.apache.org/r/13389
Fixed a performance issue in Master::Http::stats().

We spent a lot of time doing unnecessary range additions
(e.g. ports resources).

From: Jie Yu <yujie.jay@gmail.com>
Review: https://reviews.apache.org/r/13433
Ensured ExecutorInfo.framework_id is set.

This includes an update to the Scheduler Driver to set framework_id
on launchTask requests, as well as a change to the Slave to set
framework_id when generating ExecutorInfos for Command Executors.

Review: https://reviews.apache.org/r/13455
Fixed typos in scheduler.hpp and test_framework.py.

From: Yashwanth Nannapaneni <yashwanth620@gmail.com>
Review: https://reviews.apache.org/r/13448
Updated glog to 0.3.3.

This fixes a build issue with clang.

From: Vinson Lee <vlee@freedesktop.org>
Review: https://reviews.apache.org/r/13473