Improve messaging by using clang Diagnostics engine instead.
Remove unused code
Add testcase when a variable is used instead of IntegerLiteral for indicating the parameter of derivation. It should fail.
Place the diagnostic carret below the arg being diagnosed.
Try to evaluate the arg in the derived function as integer. Negative values are now successfully evaluated.
Unneeded results to compare are causing false test failures. Derivable argument is determined only by an integer value (and not via a variable) and thus some of the results to compare need to be deleted.
Synchronize error messages with the Diagnostics system.
Merge pull request #2 from mvassilev/master

Improve test diagnostics and improve derivable argument evaluation.