Add a new convenience macro for an exception handler that handles all exceptions.

When using native compiler exceptions, the previous method of doing 
this, __EXCEPT(NULL), would expand to __except( 
(NULL)(GetExceptionInformation())) which doesn't compile as NULL isn't a 
function.

So add a new macro, __EXCEPT_ALL, which works correctly both when using 
native compiler exceptions and without and which makes the meaning of 
code in which it is used clearer.