Fixed example tests to use temporary work directory for slaves.

Review: https://reviews.apache.org/r/15741/
Added 'metadata' to the replicated log to support log recovery (and
likely in the future log reconfiguration).

From: Jie Yu <yujie.jay@gmail.com>
Review: https://reviews.apache.org/r/15799
Allow HTTP requests to a slave omit "slave(1)".

Review: https://reviews.apache.org/r/15798
Fixed the ContenderDetectorShutdownNetwork test flakiness.

From: Jiang Yan Xu <yan@jxu.me>
Review: https://reviews.apache.org/r/15845
Drop messages from non-leading Masters in the scheduler driver.

Review: https://reviews.apache.org/r/15778
Added build instructions for Mac OS X Mavericks.

From: Niklas Nielsen <nik@qni.dk>
Review: https://reviews.apache.org/r/15727
Fixed master to ignore messages from unregistered framework.

Review: https://reviews.apache.org/r/15773
Reduced the minimum number of cpus per offer to 0.1.

Review: https://reviews.apache.org/r/15774
Fixed status update manager to backoff on status update retries.

Review: https://reviews.apache.org/r/15851
Fixed flaky ContenderDetectorShutdownNetwork test.

From: Jiang Yan Xu <yan@jxu.me>
Review: https://reviews.apache.org/r/15868
Made Promise::associate 'discard' in both directions.

Say you have a process defined as follows:

class FooProcess : public Process<FooProcess>
{
public:
  Future<bool> func() { return future; }
private:
  Future<bool> future;
};

Then you call dispatch that returns a future:

Future<bool> f = dispatch(process, &FooProcess::func);

If the user discards the future 'f', we expect the 'future' field in
FooProcess also being discarded. However, this is not the case
currently.

This patch fixed this issue.

From: Jie Yu <yujie.jay@gmail.com>
Review: https://reviews.apache.org/r/15319
Refactored Owned and added a function Owned::share().

From: Jie Yu <yujie.jay@gmail.com>
Review: https://reviews.apache.org/r/15731
Renamed Shared::upgrade() to Shared::own().

From: Jie Yu <yujie.jay@gmail.com>
Review: https://reviews.apache.org/r/15739
Removed Owned from stout.

From: Jie Yu <yujie.jay@gmail.com>
Review: https://reviews.apache.org/r/15837
Updated references in libprocess to use the new Owned.

From: Jie Yu <yujie.jay@gmail.com>
Review: https://reviews.apache.org/r/15838
Updated references in Mesos to use the new Owned.

From: Jie Yu <yujie.jay@gmail.com>
Review: https://reviews.apache.org/r/15839
Rewrote ZooKeeper watcher initialization using process::Once.

From: Jie Yu <yujie.jay@gmail.com>
Review: https://reviews.apache.org/r/15850
Added 'Set' wrapper in addition to union and intersect operators.

Review: https://reviews.apache.org/r/15882
Added stout 'Set' tests to libprocess/3rdparty Makefile.

Review: https://reviews.apache.org/r/15883
Added 'Some'.

Review: https://reviews.apache.org/r/15884