Directory iteration components were moved to separate files to simplify
maintenance of operations.hpp/cpp.
directory_iterator implementation on POSIX platforms has been reworked
to only allocate internal buffer when readdir_r is used. When readdir
is used, the dirent structure returned by readdir is used directly, which
eliminates the potential of buffer overrun in case if some directory name
exceeds the buffer size. This also removes the need to copy dirent members
into the buffer, which improves performance and simplifies maintenance.
For buffer size we now use the max path size as opposed to max filename
size. This is done to minimize the possibility of buffer overruns when
readdir_r is used.
On Windows, use Boost.WinAPI to configure the default target Windows version.
This removes WINVER and _WIN32_WINNT defines in Boost.Filesystem as these
macros should be defined by Boost.WinAPI now.
Additionally, exception.hpp and directory.hpp includes in operations.hpp are
marked as deprecated as operations.hpp do not need those components. Users
are encouraged to include the new headers explicitly in their code, as needed.
