Regenerate crypt archive with Boost 1.34

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@18849 b5f69653-2bf5-0310-8201-b0dafb8e1405
Provide explanation for r18838 in comment, for the benefit of anyone who'd never seen #2367 before

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@18850 b5f69653-2bf5-0310-8201-b0dafb8e1405