[boost] Should intrusive_ptr copy constructors be declared noexcept?

Subject: [boost] Should intrusive_ptr copy constructors be declared noexcept?
From: James Yonan (james_at_[hidden])
Date: 2014-08-16 00:53:45

Currently, intrusive_ptr's copy constructors are not declared noexcept. 
  This disables the std::function small object optimization when 
intrusive_ptr objects are passed by value in a lambda closure.

The attached patch tries to fix this by making the copy constructors 
conditionally noexcept, based on the noexcept status of the 
user-provided intrusive_ptr_add_ref function.

James