(mail-hist-current-header-name): Use mail-text-start.
(mail-hist-forward-header): Use mail-header-end.
(mail-hist-current-header-contents): Use mail-header-start.
(mail-hist-put-headers-into-history): Use mail-text-start.
(mail-hist-put-headers-into-history): wrap relevant body in a
`save-excursion'.
(mail-hist-add-header-contents-to-ring): doc fix.
Use `mail-hist-text-size-limit' directly.
(mail-hist-text-size-limit): doc fix.
(mail-hist-text-too-long-p): removed, we don't need this func.
(mail-hist-forward-header): move to point just after colon, don't try
to treat whitespace specially.
(mail-hist-next-or-previous-input): new func, abstracts two funcs
below.
Error informatively if not in a header.
Compensate for the extra SPACE char in "virgin" headers.
(mail-hist-next-input): just call above.
(mail-hist-previous-input): same.
(mail-hist-header-virgin-p): new func.
(mail-hist-text-too-long-p): New func.
(mail-hist-add-header-contents-to-ring): call above; if the text is
too long, then store the empty string in the history.
