sync: fix include path

git-svn-id: http://svn.boost.org/svn/boost/trunk@86257 b8fc166d-592f-0410-95f2-cb63ce0dd405
Optimize copying of allocator-free cpp_int's via memcpy.
Fix consistency of checks for exponents < 0 in powm.
Fixes #9231.
Refs #9236.

git-svn-id: http://svn.boost.org/svn/boost/trunk@86258 b8fc166d-592f-0410-95f2-cb63ce0dd405