[boost] Master branch is open again - for bug fixes, doc updates, etc

Now that we've shipped the 1.59.0 beta, the master branch is open again for updates. Please do not add new features, etc to the master until after the release. But bug fixes, documentation updates, etc are very welcome. Note that: * GCC 5.2 was released today * VS2015 should be out next week * Clang 3.7 branched for release this week Compatibility with these new compiler releases would be a good thing :-) -- Marshall