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Reorder the bug fixes for 8.5.0 to be in numeric order.
This is consistent with how the others are arranged.

Add a "current_line" local variable in the re-treeification logic in eval_sequence.
Before it was using the global variable "this_line", but not for any apparent reason.
This makes it structually clearer that "this_line" is not conceptually modified.

Add some comments to explain the re-treeification logic at eval_sequence.

Add a local variable "bodylist" to make the code more readable.

Add some comments to paren_expr

Add EVALTEST.DEFINEAFTERRUN.
This tests that calling a procedure that isn't defined throws an "I don't know how to" error,
but that after the procedure is defined, the calling procedure is retreeified and runs correctly.

Move the declaration of body_ptr to where it's first assigned in untreeify_body.
This makes the code easier to read.

Add EVALTEST.REDEFINEWHILERUNNING, a regression test for Bug #309.

Fix Bug #606; Running a procedure with parse error no longer leaks memory.

Restore the printing of leaked node's contents by setting the 'NODE' magic number.
I had broken this by adding memory filling for uninitialized memory.