(lm-header-multiline): fix spurious use of `cond'.

(lm-header-multiline): fix spurious use of `cond'.
(lm-with-file): Move all the find-file...kill-buffer stuff into
this macro.  Make it use `find-file-noselect' and make it kill
the buffer only if it wasn't already displayed somewhere.
(lm-summary, lm-authors, lm-maintainer, lm-creation-date)
(lm-last-modified-date, lm-version, lm-keywords, lm-adapted-by)
(lm-commentary, lm-verify, lm-synopsis): use lm-with-file.
(lm-commentary): fix to handle the case when the change log is
at the end of the file.