parameterize SBO size on boost::function

[Christopher Hite]

​http://lists.boost.org/boost-users/2009/12/54250.php

• It would be really nice to parameterize the SBO size like this:

template<typename Signature,std::size_t SBOSize=3*sizeof(void*)> 
class function; 

• Saving that it would be useful to have a constructor to allow you to change the allocator like this:

    template<typename Allocator> 
    functionN(const functionN&, Allocator);