* gash/pattern.scm (<pattern>): Remove the 'start-anchored?' and
'end-anchored?' fields.
(parse-pattern): Replace the fields with empty parts at the start or
end of the parts list.
(pattern-plain?): Instead of checking the fields, just check the
number of parts.
(pattern-match?, pattern-drop, pattern-drop-right): Do not worry about
the fields, because the empty parts ensure the right thing happens.
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