Added implementation of 64-bit atomic operations on 32-bit Windows. Pointer specializations of 64-bit CAS-based atomic implementation extracted to a separate header, since these specializations are not needed on 32-bit platforms.

svn path=/trunk/boost/atomic/; revision=84695
Code cleanup.

svn path=/trunk/boost/atomic/; revision=84699
Code cleanup.

svn path=/trunk/libs/atomic/; revision=84700