#2478 - document the need to inform the mesh of changes to element attributes in tutorials and howto.

Also fix a bug if creating an `OutputFileHandler` with a `FileFinder` when the root output folder hadn't been created yet.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@20943 b5f69653-2bf5-0310-8201-b0dafb8e1405
#2478 - update tutorial to use a `DistributedTetrahedralMesh`.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@20944 b5f69653-2bf5-0310-8201-b0dafb8e1405


git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@20947 b5f69653-2bf5-0310-8201-b0dafb8e1405
#2426 Failing test with PARMETIS_LIBRARY partitioning only. 

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@20948 b5f69653-2bf5-0310-8201-b0dafb8e1405
#2426 Test fails with this cube mesh too.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@20950 b5f69653-2bf5-0310-8201-b0dafb8e1405
#2426 Fix the PARMETIS_LIBRARY partitioner to not include unnecessary elements.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@20952 b5f69653-2bf5-0310-8201-b0dafb8e1405
#2426 The alternative way to not include unnecessary elements is more efficient.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@20953 b5f69653-2bf5-0310-8201-b0dafb8e1405