Fixed an import error in futures.py.

When queue is empty, the name Queue.Empty must be imported.

From: Du Li <lidu008@gmail.com>
Review: https://reviews.apache.org/r/15585
Fixed the flaky pstree test.
Saved KB/MB/GB bytes as constants to save multiplication.

Each time the 'dataSize' filter was called, the function did lots of
multiplication to get bytes per KB, MB, and GB to determine how to
print the string.

Moving the constants outside the function returned by the filter means
the multiplication is done only one time on app start up instead of in
each call.

* Added 1 digit to the right of the decimal point for GB. 6.5 GB is
  very different from 7 GB.

Review: http://reviews.apache.org/r/15579
Removed unnecessary wrapping .row from frameworks.

Single-column layouts in Bootstrap do not need to use .row .span-12
since width: 100% already has the same effect.

frameworks.html now matches the other tabs, slaves.html and offers.html.

Review: http://reviews.apache.org/r/15580
Added 'completed_frameworks' sorter for /frameworks.

Completed frameworks were added to the /frameworks page in commit
77c72f3639024168996ad3257908b558beed3996, but a table sorter was not
added. This makes it possible to sort the table by any of its columns.

Review: http://reviews.apache.org/r/15581
Fixed a bug in Web UI.

There was no check on the bounds of an array before attempting to read
it.

Review: https://reviews.apache.org/r/15640
Fixed the thread-safety of process::ID::generate.

Review: https://reviews.apache.org/r/15628
Fixed MESOS-243: Made ExecutorDriver.join() wait for outstanding requests.

Review: https://reviews.apache.org/r/15597
Added back the sleep call in the command executor.

Review: https://reviews.apache.org/r/15662
Moved GroupProcess into group.hpp and made it a public member of
Group for testing.

From: Jiang Yan Xu <yan@jxu.me>
Review: https://reviews.apache.org/r/15221
Added local timeout so that Group operations fail after
we locally determine that the session is timed out.

From: Jiang Yan Xu <yan@jxu.me>
Review: https://reviews.apache.org/r/15016
Fixed a bug where Group::cancel can return a failed future
if the membership is already cancelled.

The API stipulates that a successful Future<bool> but with 'false'
value should be returned.

This can happen when:
1) The cancel() operation is queued up due to connectivity issue but
then invoked again by sync() the membership could be gone.
2) Even if not delayed, in cancel() we first checked whether the
membership exists in our local cache but the membership could have
expired by then (or when we invoke zk->remove(...)) but we have yet to
receive the update for it.

From: Jiang Yan Xu <yan@jxu.me>
Review: https://reviews.apache.org/r/15487
Added Zookeeper leader contender and detector abstractions.

From: Jiang Yan Xu <yan@jxu.me>
Review: https://reviews.apache.org/r/13086
Increased the minimum number of threads that libprocess statically
allocates.

From: Jiang Yan Xu <yan@jxu.me>
Review: https://reviews.apache.org/r/15658
Added Master contender and detector abstractions.

From: Jiang Yan Xu <yan@jxu.me>
Review: https://reviews.apache.org/r/13087
Replaced usage of old detector with new Master contender and detector
abstractions.

From: Jiang Yan Xu <yan@jxu.me>
Review: https://reviews.apache.org/r/15510
Fixed a flaky test: SlaveRecoveryTest.ShutdownSlave.

Review: https://reviews.apache.org/r/15664
Python CLI helper 'http.get' should not assume JSON.

Review: https://reviews.apache.org/r/15684
Merge branch 'cli-http-get'
Bug fix in Python CLI futures.

Review: https://reviews.apache.org/r/15691