#1902 add containers for communication and communication method to `NodeBasedCellPopulation` and a `SendRecv` method to `ObjectCommunicator`.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@18123 b5f69653-2bf5-0310-8201-b0dafb8e1405
#1902 forgot to add new files.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@18124 b5f69653-2bf5-0310-8201-b0dafb8e1405
#2130 Allow for new mallocs on `TestSimpleNonlinearEllipticSolver::Test2dOnUnitSquare()`

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@18125 b5f69653-2bf5-0310-8201-b0dafb8e1405
Fix acceptance broken by r18122/#1660

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@18126 b5f69653-2bf5-0310-8201-b0dafb8e1405