Updated WhitelistWatcher to watch only if a file is given.

Whitelist may be represented either by a filepath or a by a wildcard.
In the latter case WhitelistWatcher should not constantly try reload
the whitelist.

Review: https://reviews.apache.org/r/28442
Removed some DiskInfo validations from C++ Resources in favor of doing
them in the master.

Review: https://reviews.apache.org/r/28429
Fix extra space in fetcher code.
Fixed coding style issue in Node class

Removed the space between & and the parameter type

Review: https://reviews.apache.org/r/28382
Expanded labels comment in mesos.proto.

Review: https://reviews.apache.org/r/28444
Adds Coursera to Mesos adopters list.
Rename Socket::read to Socket::recv.

This is more consistent: send/recv vs. send/read.

Review: https://reviews.apache.org/r/28484
Renamed poll.cpp to libev_poll.cpp.

Review: https://reviews.apache.org/r/28314
Extended install() to support more arguments.

Review: https://reviews.apache.org/r/28363
Refactored task launching in the master.

This adds addTask(), which is similar to addSlave() and addFramework().
The benefit is that we allow the caller to add the task and have control
over when the RunTaskMessage is sent.

Review: https://reviews.apache.org/r/28364
Fixed a double counting bug for staging tasks.

Review: https://reviews.apache.org/r/28433
Removed the empty resource check in master.

Review: https://reviews.apache.org/r/28616
Removed unnecessary 'whitelisted' variable in the allocator.

Review: https://reviews.apache.org/r/28662
Cleaned up the utility structs in the allocator.

Review: https://reviews.apache.org/r/28663
Updated Allocator::slaveAdded to take the total resources explicitly.

Review: https://reviews.apache.org/r/28665
Updated allocator.hpp to idiomatically use the "Process wrapper" pattern.

Review: https://reviews.apache.org/r/28666
Cleaned up the allocator method naming.

Review: https://reviews.apache.org/r/28667
Fixed a bug in the allocator's framework activation.

Review: https://reviews.apache.org/r/28668
Updated allocator to only check initialization in exposed methods.

Review: https://reviews.apache.org/r/28669
Fixed a compiler warning from clang.