Minor type traits update

From: John Maddock (John_Maddock_at_[hidden])
Date: 2001-03-27 07:01:00

The following types have been added to the type traits library:

is_function
add_const
add_volatile

In addition there are some misc fixes:
is_const/is_volatile now compile/work with reference types.
Most of the templates now compile and work correctly with
abstract/incomplete/function types, but only provided the compiler supports
partial specialisation.  The only templates that don't work with these
types are alignment_of and is_convertible, but that can be considered to be
"by design" (think about it).

Thanks to every one that's commented on this.

- John Maddock
http://ourworld.compuserve.com/homepages/john_maddock/