#2517 Beef up a bidomain test and fix a bug made apparent by said test (needed to initialise cache suitably). 
Added an exception when asking for a tensor from an element out of range (previously a default was returned!).
Also removed an almost identical monodomain test as we now test the same functionality in the bidomain one.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@21504 b5f69653-2bf5-0310-8201-b0dafb8e1405
#2488 tidying

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@21505 b5f69653-2bf5-0310-8201-b0dafb8e1405
#2517 Don't need this modifier any more, all in TestBidomainTissue.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@21506 b5f69653-2bf5-0310-8201-b0dafb8e1405