Basic rvalue and C++11 support

[Antony Polukhin]

This patch adds variant(variant&&), variant& operator=(variant&&) and template <class T> variant& operator=(T&&) functions to Boost.Variant for compilers with rvalue references support (rvalue emulation via Boost.Move is not used for compatability reasons).

template <class T> variant& operator=(T&&) function is enabled only if T&& is a rvalue reference.

Patch is constructded via copying original assign functions and adding move semantics to them. Example: Visitor copy_into was copied as move_into. Copy constructors in internal_visit functions were replaced by move constructors.

If compiler supports rvalue references, std::move is imported to namespace ::boost::detail::variant (this also worked around bug with unqualified call to move() in MSVC2010)

BOOST_NOEXCEPT modifiers added to some methods.

This patch improves performance up to 6 times for some operations. Was tested on GCC-4.6 (with and without c++11 mode) and MSVC2012.

[Antony Polukhin]

Boost.Test for rvalue support of variant

[Antony Polukhin]

Performance test for new rvalue methods

[Antony Polukhin]

(In [81293]) Added basic rvalue support and marked some functions with BOOST_NOEXCEPT (#refs #7620)

[Antony Polukhin]

(In [81455]) Merge from trunk: added basic rvalue support and marked some functions with BOOST_NOEXCEPT (fixes #7620)

[Antony Polukhin]

(In [81456]) Merge from trunk: merge performance tests (refs #7620)