1. Fixed compilation with MSVC 2003.
2. Fixed incorrect reinterpret_casts in constexpr constructors that could result in buffer overruns. The initializing constructors for non-integral atomics are not constexpr yet because memcpy must be used inside.
3. Made atomic_flag default constructors constexpr. This is not by the standard but we do not implement ATOMIC_FLAG_INIT yet, so the default constructor is needed and it should be constexpr when possible.
4. Fixed a few syntax errors and cleaned up the code a bit.
5. Moved operator value_type() to the interface class in order not to duplicate it in base_atomic specializations.
6. The return type of operator=() changed to follow the standard.

svn path=/trunk/boost/atomic/; revision=83096