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.
Splitted resource and resource usage checkers.

Review: https://reviews.apache.org/r/28618
Added basic DiskInfo check in master.

Review: https://reviews.apache.org/r/28626
Added tests for basic DiskInfo checker.

Review: https://reviews.apache.org/r/28627
Added duplicated persistence id check in ResourceChecker.

Review: https://reviews.apache.org/r/28664
Renamed task and offer visitors to validators.

Review: https://reviews.apache.org/r/28684