(Rmail Deletion): Revert previous change, which was

(Rmail Deletion): Revert previous change, which was
describing the Rmail summary versions.
(Rmail Reply): Give more details of rmail-dont-reply-to-names.
Minor re-wording for rmail-resend.
(Rmail Make Summary): Summaries apply to buffers rather than files.
<rmail-summary-by-topic>: Headers includes the subject.
<rmail-summary-by-recipients, rmail-summary-by-topic>: Give more
details, including prefix arguments.
Not counting lines might be faster.
(Rmail Summary Edit): More details on the delete commands.
Add rmail-summary-bury.
(Rmail Display): Mention rmail-displayed-headers.  Fix typo.
Simplify rmail-highlighted-headers description.  Update face name.