compiler/prog_item.m:
Delete item_nothing as an alternative in the item type.
These items never occur in parse trees, being handled fully at the time
when the parse tree is constructed. Nevertheless, their presence in
the item type required code that handles parse trees to worry NOW about
how they should handle item_nothings in case a possible future change
let them survive the parse tree construction process.
compiler/parse_types.m:
Replace item_nothing with iom_handled in the item_or_marker type,
whose values are used only during the parse tree construction process.
The replacement is significantly simplified compared with the original,
containing only the functionality that our current use cases need.
compiler/parse_error.m:
Remove rme_warn_item_nothing from the read_module_error type.
It was being added to error sets, but nothing ever tested for its presence.
Its task as a signifier of the presence of a compilation-stopping error
now belongs to the severity of the associated error_specs.
compiler/parse_item.m:
Fix the logic of the code that decides whether the format of the
version_numbers_map item is recorded in an obsolete format
(i.e. whether its *own* version is too old). Specificially,
treat non-numerical "version number" terms as being malformed,
not as being obsolete.
compiler/canonicalize_interface.m:
compiler/check_raw_comp_unit.m:
compiler/comp_unit_interface.m:
compiler/equiv_type.m:
compiler/get_dependencies.m:
compiler/item_util.m:
compiler/make_hlds_separate_items.m:
compiler/module_qual.collect_mq_info.m:
compiler/module_qual.qualify_items.m:
compiler/modules.m:
compiler/parse_module.m:
compiler/parse_pragma.m:
compiler/parse_tree_out.m:
compiler/prog_item_stats.m:
compiler/recompilation.check.m:
compiler/recompilation.version.m:
Conform to the changes above.
