modified install instruction for boost on windows
Merge branch 'boost_onwindows' into hotfix-boost-win2

Conflicts:
	superbuild/External-Boost.cmake
Use boost 1.56

compilation errors are fixed for XCode >= 5.1
Updated include dir
on msvc, boost.thread also depends on boost.date_time

https://svn.boost.org/trac/boost/ticket/7045
Merge pull request #119 from statismo/hotfix-boost-win2

Hotfix boost win2 for master