Add noexcept to conform with C++11 after #7278

[viboes]

The ticket #7278 introduce some noexcept in virtual functions that makes derived classes overriding these functions to use BOOST_NOEXCEPT. The patch attached includes the needed changes for asio.

[chris_kohlhoff]

(In [82290]) Merge from trunk:

• Fix some 64-to-32-bit conversion warnings. Fixes #7459

• Fix typos in comments. Fixes #7761

• Fix error in example embedded in basic_socket::get_option's documentation. Fixes #7562

• Use long rather than int for SSL_CTX options, to match OpenSSL. Fixes #7209

• Use _snwprintf to address a compile error due to the changed swprintf signature in recent versions of MinGW. Fixes #7373

• Fix deadlock that can occur on Windows when shutting down a pool of io_service threads due to running out of work. Fixes #7552

• Enable noexcept qualifier for error categories. Fixes #7797

• Treat errors from accept as non-fatal. Fixes #7488

• Add a small block recycling optimisation.

• Version bump.

• Regenerate documentation.