Added 'active_tasks' stat to master stats endpoint.

Review: https://reviews.apache.org/r/17442
Added queued and launched tasks to slave stats.

Review: https://reviews.apache.org/r/17443
Updated upgrades document for 0.17.0.

From: Jie Yu <yujie.jay@gmail.com>
Review: https://reviews.apache.org/r/17473
Updated the CHANGELOG for 0.17.0.

From: Jie Yu <yujie.jay@gmail.com>
Review: https://reviews.apache.org/r/17474
Updated configure.ac to 0.18.0.
Added LLDB convenience scripts.

This patch adds lldb-mesos-tests, lldb-mesos-local, lldb-mesos-master
and lldb-mesos-slave in similar style as gdb-mesos-* as GDB seems to
have been out phased on OS X Mavericks.

Review: https://reviews.apache.org/r/17445
Added a missing lock acquisition in /__processes__.

Review: https://reviews.apache.org/r/17519
Updated the semantics of Clock::resume.

Now Clock::resume results in the resumption of time from the state
of Time when resume is called, rather than re-winding time back to
real time.

This requires an update to Time::create to take into account the
advanced state of time.

Review: https://reviews.apache.org/r/17480
Fixed the use of a raw unix time in the Slave.

This updates the slave to use Time::create to ensure the modification
time matches the current time frame in libprocess.

Review: https://reviews.apache.org/r/17481
Added a child Reaper utility in libprocess.

Review: https://reviews.apache.org/r/17304
Update the slave to use the libprocess Reaper.

Review: https://reviews.apache.org/r/17305
Added an asynchronous subprocess utility.

Review: https://reviews.apache.org/r/17306
Adds Ignidata to Powered by Mesos list.
Adds to and alphabetizes list of software frameworks on Powered By page.
Updates link to Aurora documentation on docs home.
Fixed the flaky Os.killtree test.

Review: https://reviews.apache.org/r/17558
Sped up tag and vote scripts by not compiling the whole of mesos.

Review: https://reviews.apache.org/r/17598
Fixed MPI framework.

MPI did not run on Mesos due to broken version-dependent paths and
broken reg exp in python scheduler script that failed to extract
ip and port of mpd processes. Corrected the above.

(An effort is underway to support the hydra process management
 facility in lieu of the deprecated mpd...)

From: Bernd Mathiske <bernd@mesosphere.io>
Review: https://reviews.apache.org/r/17635
Adds Medidata Solutions to 'Powered by Mesos' list.
Fixed a compilation issue in Subprocess.