git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19160 b5f69653-2bf5-0310-8201-b0dafb8e1405
#1157 Pull out an XDMF master file writing method

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19161 b5f69653-2bf5-0310-8201-b0dafb8e1405