Since expression outputs are now actually defined, make use of this fact.

Since expression's outputs now generally work with their type correctly, make
use of this to try and ensure an expression is evaluated correctly.  Also
make sure that the requested type does match the type outputted, and test
that this occurs (for now, just in BinaryExpression and Variable).

git-svn-id: https://groke.mcmaster.ca/svn/grad/colin/branches/TableTool_javization@10538 57e6efec-57d4-0310-aeb1-a6c144bb1a8b