[boost] [config] BOOST_DISABLE_THREADS defined by Boost.Config

From: Peter Dimov (pdimov_at_[hidden])
Date: 2008-04-03 13:38:49

Joe Gottman quite correctly points out in

http://svn.boost.org/trac/boost/ticket/1762

that shared_ptr should honor user definitions of BOOST_DISABLE_THREADS and 
disable MT support.

Unfortunately, despite documenting quite clearly that BOOST_DISABLE_THREADS 
is a user macro, Boost.Config defines it in some situations. This means that 
I can't rely on this macro to reflect the user's intent, as I don't know 
whether it's been set explicitly by the user, or implicitly (and incorrectly 
IMO) by Boost.Config.