cpp11-migrate: Add Replace-AutoPtr Transform

Summary:
Add a new transform to replace uses of 'std::auto_ptr' by 'std::unique_ptr'.
Copy-ctor and assign-operator are wrapped with a call to 'std::move()'.

Note that until header modification is ready it is not that useful, that's why
it's marked as (EXPERIMENTAL) in the command line description and a "Known
Limitations" section is present in the transform documentation.

Reviewers: revane

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1074
Merge branch 'replace-auto_ptr' of github.com:Sarcasm/clang-tools-extra into replace-auto_ptr

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