This is the first of several large commits changing several aspects of
the handling of defaults. The overall main purpose of these changes is
to protect against using non sensible values in the case the values have
not been sensibly specified in the deck. The changes in this commit
include:
1. The "default default" values to be used when an item without an
explicit default are defaulted are removed completely.
2. If a ParserItem is queried for a default value when no default has
been assigned it will raise an exception.
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