FMSLogo Code

Simplify the memory management in err_logo from ref/vref/deref to a single gcref().

Fix the reference to bug #605 (I had mistakenly thought it was bug #603).

Enable another regression test for Bug #603, now that it has been fixed.

Fix Bug #603; "APPLY [[] [] abc ] []" no longer crashes FMSLogo

The fix was to move the "list of lists" check that is used
in define_helper to the anonymous_function() code path.

Rework setitem_helper() not to modify the arguments list.
The resulting code is simpler.
This is part of a larger effort to reduce the use of side effects in the code base.

Refactor setitem_helper to use assign() instead of duplicating its logic.
This makes the code a little shorter and a little more readable.

Refactoring: Change setitem_helper to call int_arg instead of integer_arg() and getint().
This is a little simpler and doesn't have side-effects.

Make RUNRECOVERABLEERRORTEST log that it outputs 1 when :erract is called more than expected.
I had forgotten that it did that and was mystified by some behavior when writing new tests.

Add tests for SETITEM.

Refactoring: Rewrite litem() to use get_int() instead of get_integer().
This is more direct and requires less code.