#2370 We decided the !AbstractContractionCellFactory should be a separate inheritance structure - largely because the mesh is different!

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19020 b5f69653-2bf5-0310-8201-b0dafb8e1405
#2367 Fix the heart (ionic models) floating point exceptions.  These were caused by either deliberately driving a model to an non-physiological voltage or accidentally leaving a stale value in `mFixedVoltage`.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19023 b5f69653-2bf5-0310-8201-b0dafb8e1405