Break compatibility with pre-C++11, implement make_unique

Martin Heistermann requested to merge make_unique into master

@moebius, @lyon - if I understood you correctly, OVM and OM shall also be C++-11-and-up? If so, we can avoid some more ifdef complexity by just breaking compatibility now. (If not, I'll revise my make_unique patch)

Let me know if you'd prefer separate PRs.

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