RFC: change in policy for include guards

Hi all,
  there are two topics I'd like us to discuss about to share an
agreement when the right time comes. I'm spreading the discussion over
two threads in order not to cross wires and facilitate discussion.

The topic I'm thinking of is the policy of autoconf-detecting some
system headers we use. While this is undoubtably good for C- and
system- headers, it doesn't make much sense for pure C++ headers,
which are very strongly defined by the standard and for which there is
no compatilibty wrapper. In these cases, making the include
conditional will only result in a less-readable error message when the
build eventually fails.

What do you think?

-- 
    Kinkie