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Add more test coverage for when ZOOM is given bad input.

Rename nonnegative_flonum_arg to nonnegative_flonum_arg.
Also, change it to take the argument, instead of modifying the argument list.
This follows the example of flonum_arg and makes it easier to call,
as the caller no longer has to extract the FLONUM from a numeric NODE.

This is part of a larger effort to reduce the number of side effects within the code base.

Fix a test bug in WAITTEST.BADINPUT.RECOVERABLE.
It incorrectly and misleadingly reported that WAIT output a value, when the value came directly from :erract because WAIT (correctly) didn't output one.

Fix an incorrect claim in the comment for flonum_arg.

Add more regression tests for WAIT, particularly for bad input and recovery of bad input.

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.