Vesta Configuration Management System

In the result of _run_tool, a value of FALSE is used for a file deleted by
the tool. Sometimes people take the result of _run_tool and simply ++ it
into ./root. This can give you a value of FALSE in the input of a
_run_tool call, which will give you errors if the tool tries to access the
path in question.

It would be nice if the evaluator's ToolDirectoryServer treated FALSE as
though the name was not present at all (i.e. honoring a previous tool's
deletion). This would be a little favor to the SDL programmer, eliminating
the need to clean the FALSE values out of a _run_tool result before merging
it into the filesystem for a later tool. This should be pretty easy to
implement, though some care should be taken with dependencies. It's a
little counter-intuitive, but the _run_tool call would actually depend on
the FALSE value even though the tool process itself would never see it.

This could be considered a repeatability problem. Previous versions of the
evaluator would generate a response that the tool would see as a filesystem
error. I don't see this as a big problem, as I don't think any useful
builds could depend on that behavior.