Mark constructors/assignment/swap noexcept where possible

[Lastique]

Please mark functions noexcept where possible for the types provided by Boost.Interprocess. In particular, I'm interested in types shared_memory_object and mapped_region, but this is probably not limited to those.

The functions that have immediate benefit from being marked are:

• Default constructors.
• Move constructors and assignment.
• Copy constructors and assignment, where possible.
• swap.

The important effects of this markup includes:

• More efficient implementation of standard containers and algorithms.
• Implicitly defined constructors and operators of user's types that have Boost.Interprocess types in members or base classes become noexcept.

[igaztanaga]

Many thanks for the report!