Log Message:
Update to 2.2.8

Changelog:
Version 2.2.8 (16 July 2014)
-------------

        Correct testing of minimum values in Extension::real_to_double()
        and Extension::list_to_vector_double() (extension.h).

        Deal properly with unexpected out-of-memory conditions in
        executing Extension::exec() and Extension::exec_shared()
        (extension.h).

        Minor code refactoring in EmitterArg::connect() and
        SafeEmitterArg::connect() (emitter.h).

        Update documentation (callback.h, emitter.h, extension.h,
        notifier.h, parallel.h, task_manager.h).