Fixed build error caused by overloading socket call on CentOS 5.

Review: https://reviews.apache.org/r/28854
Modified mesos configure.ac to set $with_svn to `brew --prefix subversion` for OS X.

Review: https://reviews.apache.org/r/28721
Modified libprocess configure.ac to set $with_svn to `brew --prefix subversion` for OS X.

Review: https://reviews.apache.org/r/28722
Added a hash function for Node.

Review: https://reviews.apache.org/r/28869
Fixed a long-standing performance issue in libprocess' SocketManager.

Review: https://reviews.apache.org/r/28838
Extended error message for module manager when library loading fails.

Review: https://reviews.apache.org/r/28764