Fixed hard tabs in monitor.cpp

From: Niklas Nielsen <nik@qni.dk>
Review: https://reviews.apache.org/r/15500
Fixed string leaks in os.hpp.

From: Niklas Nielsen <nik@qni.dk>
Review: https://reviews.apache.org/r/15368
Added list of TaskStatuses to Task message.

Task now includes repeated task status with timestamps.  This permits
caltulating the start/finish time for tasks (among other things).

To support this, a timestamp was added to the TaskStatus message which
is also passed to frameworks when there are state transitions.

Review: https://reviews.apache.org/r/14434
Normalized task start/finish time in Web UI.

Review: https://reviews.apache.org/r/15539
Added terminated frameworks to frameworks tab.

In preparation for moving frameworks off the homepage, terminated
frameworks will now be listed on /frameworks.html.

The code was copy/pasted from home.html.

Review: http://reviews.apache.org/r/15526
Moved offers to their own tab and page.

In preparation for moving Tasks to the homepage, Offers moved to their
own page and tab. They are available as top-level navigation, and the
homepage table is now gone.

Review: http://reviews.apache.org/r/15527
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