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Add EVALTEST.ERASEWHILERUNNING.
This is a focused test for a specific clause in a if statement in eval.cpp.

Cleanup: Stop calling untreeify_procnode() in release_all_objects()
This is no longer needed, now that treeifying a procnode no longer creates circular references.

Fix Bug #620; APPLY no longer leaks when running named slot templates.

The fix is not to make LINE nodes when treeifying a procedure.
In the context of a treeified procedure, LINE nodes would create a cycle
that would leak memory unless the procedure is explicitly untreeified.

In the case where APPLY was given named slot templates (a body list),
APPLY creates an anoymous procedure and there's no good place in the
evaluator to untreeify it. In this case, some nodes were leaked.

This was a regression introduced by r1570, when an untreeify_line
was removed from the logic for treeifying a proceedure, following what
UCBLogo does. However, UCBLogo doesn't leak nodes because
it has a mark-and-sweep garbage collector that can handle cycles.

The new fix doesn't re-add the explicit untreeification. Instead, it
extracts a helper function from untreeify_line() that doesn't mark the
line as a TREE or create the cycle. To me, it makes more sense not to
create the cycle than to create a cycle then immediately undo that work.

Include the reference count of nodes in debug_dump_node.
This helps to debug some memory leaks and freed memory reads/writes.

Replace a NIL with nullptr for something that isn't a NODE*.
nullptr is more correct, since NIL is only supposed to be for a NODE *.

Fix build breaks when USE_PRECOMPILED_HEADER is not defined.

Mark the build as non-official

Remove settree__tree().
This had an unstated side effect of setting the treepair's generation.
Worse, the generation had to be immediately modified by all callers, which convinced me that it'd would be better for the callers to construct the treepair.

Cleanup: Remove unneeded local variable "s" in cnv_node_to_numnode.

Cleanup: Remove logic to skip over the leading + in cnv_node_to_numnode.
This was dead code because numberp() doesn't allow numbers to begin with a +.