Make it configurable if the client should search for unread
parents or relatives of a text before displaying it. Also, add a new strategy ('oldest-ancestor) that only searches among parents. Details: * vars.el.in (kom-read-related-first): New configuration variable. Set this to nil to get the old-style behaviour, 'oldest-related to get the behaviour before this commit, or 'oldest-ancestor to get the new default behaviour. * lyskom-rest.el (lyskom-find-lowest-text): Moved internal documentation from the doc-string to an internal comment. (lyskom-find-unread-ancestor): New defun. This code is based on lyskom-find-lowest-text, but works in a more sensible way. (lyskom-select-text-to-read): New defun, extracted from kom-view-next-text. Handle the new oldest-ancestor strategy. (kom-view-next-text): Use lyskom-select-text-to-read to simplify the code. * swedish-strings.el, english-strings.el (lyskom-custom-strings): Added ancestor, relative, kom-read-related-first-doc and kom-read-related-first-tag. * option-edit.el (lyskom-customize-buffer-format): Added kom-read-related-first. (lyskom-custom-variables): Ditto.