#1360 Document some suppressed warnings.  Also tidy some `UblasCustomFunctions`

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19145 b5f69653-2bf5-0310-8201-b0dafb8e1405
Fix build broken by r19145

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19146 b5f69653-2bf5-0310-8201-b0dafb8e1405