Removed unreliable setsid test from subprocess_tests.

Removed an unreliable test from subprocess_tests as it was expecting a
specific order of events without syncing, hence super flaky.

Review: https://reviews.apache.org/r/20023
Updated the "High Availability" doc to reflect the master detector refactoring in Mesos 0.16.0.

Review: https://reviews.apache.org/r/18155
Modifed getHostName to use the correct error code.

Review: https://reviews.apache.org/r/20055
Updated the fetcher subprocess to pass in the environment explicitly.

Review: https://reviews.apache.org/r/19164
Fixed a call to delete where delete[] should have been used.
Added support for constructing a Future from a Try.

Review: https://reviews.apache.org/r/20106
Added 'make bench' make target to run benchmark tests under 'src/'.

- The 'benchmark' tests are the GTEST test cases or tests with the name containing 'BENCHMARK_'.
- The tests can be inovked by 'make bench' command or 'make check' with a non-zero environment variable MESOS_RUN_BENCHMARKS value.

Review: https://reviews.apache.org/r/20017
Added JobServer to the list of job schedulers that are implemented as Mesos
Framework.

This closes #13.

Review: https://github.com/apache/mesos/pull/13
Added link to Javadoc and reorganized framework developer links.

Review: https://reviews.apache.org/r/20004
Used implicit Try -> Future flattening in the Slave.

Review: https://reviews.apache.org/r/20178
Undid the line wrapping for email template in release script.
Made os::system async signal safe.

Review: https://reviews.apache.org/r/20127
Added a few methods for net::MAC and net::IP.

Review: https://reviews.apache.org/r/19982
Updates download version listed in Getting Started guide to 0.18.0
Fixed process::await and process::collect to take const references.

Review: https://reviews.apache.org/r/20231
Added a metrics API.

Review: https://reviews.apache.org/r/18718
Removed timeouts in interfaces in favor of Future::after.

Review: https://reviews.apache.org/r/19672
Used Future::after in Network.

Review: https://reviews.apache.org/r/19674
Cleaned up master detector usage in tests.

Review: https://reviews.apache.org/r/19834
Refactored State::names to return a set instead of vector.

Review: https://reviews.apache.org/r/19835