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Fix a typo in a test failure message.

Add comments to explain a mysterious block of code in evaluator() as well as a test that exercises it.

Add tests for SETPOS.

Simplify release_all_objects() by removing unneeded logic that set object properties to NIL.
This makes the code easier to understand as each line now has purpose.

Add flonum_arg(), which is a replacement for float_arg() that:
1) Doesn't have the side effect of modifying its input list on error.
2) Accepts the argument, instead of the list containing the argument.

It also changes lform() to use the new function to provide that it's correct.

This is part of a larger effort to simplify by the code base by reducing the number of unneeded side effects.

Add more tests for FORM, including tests that use :erract to fix bad input.

Fix a comment

Add the results of some new test cases that were added to test/eval.lgo

Refactoring: Change ACTIVEAREATEST.PERSISTTEST to use RUNLOGOPROGRAM instead of duplicating its logic.
This makes the test a little shorter, and therefore more readable.

Refactoring: Slightly simplify the logic for handling the return value of a macro.

This moves:
if (unev == Unbound)
{
assign(unev, NIL);
}

To the branch where this change matters.

It also precomputes its effect instead of assigning env twice.

Note that I haven't confirmed that unev can be Unbound.