MESOS-1857 Fixed path::join() on older libstdc++ which lack back().

Review: https://reviews.apache.org/r/26256
Added functionality to create SVN based diffs of arbitrary strings.

See summary.

Note that this hard codes the location of the subversion and Apache Portable Runtime (APR) headers.

Review: https://reviews.apache.org/r/24535
Added DIFF to the replicated log state storage implementation.

See summary.

Note that this hard codes the location of the subversion and Apache Portable Runtime (APR) headers.

Review: https://reviews.apache.org/r/24536
Updated metrics::Timer::stop to return elapsed time.

See summary.

Review: https://reviews.apache.org/r/24537
Add build config for svn and apr libraries

Review: https://reviews.apache.org/r/26214