#2016 - fix a parallel test failure

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@20342 b5f69653-2bf5-0310-8201-b0dafb8e1405
A useful `Debug/PetscTools` macro for debugging on big iron. 

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@20371 b5f69653-2bf5-0310-8201-b0dafb8e1405