How do I tell if the new type_traits stuff is available

[Patrick Horgan]

Our software is only built with gcc, but on various architectures.  
We've been using the boost type_traits including enable_if, is_integral, 
et.al.  As time goes forward, I'd like to switch the the standard 
versions of these same things.  How do I detect that they are available 
at compile time so I can import them into my namespace either from std 
if available, or boost if not?

Patrick