Added a shared pointer abstraction which enforces const accesses.

From: Jie Yu <yujie.jay@gmail.com>
Review: https://reviews.apache.org/r/14848
Change Web UI to use /master/redirect for leader redirection.

The leader address from master/state.json does not undergo the same
name lookup as the master/redirect end point. This becomes a problem
during redirect in the webui when internal IPs are used.

Changing location of the redirect to '/master/redirect' solves the
immediate problem.

From: Niklas Nielsen <nik@qni.dk>
Review: https://reviews.apache.org/r/14859
Revert "Fixed ARG_MAX compilation issue on some POSIX systems."

This reverts commit d8da5f4d17d3a673beb5b76d0a7370bdda99c51d.

Review: https://reviews.apache.org/r/14860
Revert "Added a missing include."

This reverts commit b9e6ce6e9ccbf08ae8a6a666c09391b407a3d82a.

Review: https://reviews.apache.org/r/14861
Revert "Updated the balloon tests to test the memory threshold."

This reverts commit ebba5c109d17fac2a18c16467097846f398e7217.

Conflicts:
	src/examples/balloon_framework.cpp
	src/tests/script.cpp

Review: https://reviews.apache.org/r/14862
Revert "Added memory threshold notifications for inducing OOMs."

This reverts commit 8d742395b77cb9fb95cf5fdc123545aeb69f5c48.

Review: https://reviews.apache.org/r/14863
Fixed mesos.pom to work from inside the build directory.

Review: https://reviews.apache.org/r/14706
MESOS-518: Improve README with Markdown
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/mesos
Removed hard tabs in libprocess.

From: Niklas Nielsen <nik@qni.dk>
Review: https://reviews.apache.org/r/14720
Removed hard tabs in zookeeper related code.

From: Niklas Nielsen <nik@qni.dk>
Review: https://reviews.apache.org/r/14721
Removed hard tabs in the Mesos code.

From: Niklas Nielsen <nik@qni.dk>
Review: https://reviews.apache.org/r/14722
Improved Duration output operator.

1) handle negative durations.
2) try to find a whole number to print out.

From: Jiang Yan Xu <yan@jxu.me>
Review: https://reviews.apache.org/r/11331
Added --hostname flag to slave and removed webui_hostname.

A slave can be started with --hostname which explicitly sets hostname
instead of usual system hostname. This is necessary in situations
where system hostname resolves to internal names which cannot be
accessed from the web ui.

From: Niklas Nielsen <nik@qni.dk>
Review: https://reviews.apache.org/r/14847
Refactored slave recovery to make reading checkpointed data asynchronous.

Review: https://reviews.apache.org/r/14616/
Added os::utime() to update access/modification times.

Review: https://reviews.apache.org/r/14662/
Fixed slave gc to use modification time for old directories.

Review: https://reviews.apache.org/r/14663
Fixed slave to properly recover latest run of completed executors.

Review: https://reviews.apache.org/r/14910
Changed slave to do checkpointing by default.

Review: https://reviews.apache.org/r/14896
Fixed tests to disable checkpointing by default.

Review: https://reviews.apache.org/r/14913