Updated Boost to version 1.57.0.
Merge remote-tracking branch 'origin/next' into MAID-432_boost_1_57

Conflicts:
	cmake_modules/add_boost.cmake
Merge remote-tracking branch 'upstream/next' into MAID-432_boost_1_57
Merge pull request #169 from Fraser999/MAID-432_boost_1_57

Updated Boost to version 1.57.0.
Merge branch 'next' of https://github.com/maidsafe/MaidSafe into next
SHA stamp by Jenkins as building correctly