#2411 #2016 #2349.  Fix reading failing test for MacOS to be compiler independent and include a valuable assertion.  Make robust failing test for 3-digit exponents.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19505 b5f69653-2bf5-0310-8201-b0dafb8e1405
#2349 Fix reading with underflow

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19506 b5f69653-2bf5-0310-8201-b0dafb8e1405