(allout-doublecheck-at-and-shallower): Clarify docstring.

(allout-doublecheck-at-and-shallower): Clarify docstring.
(allout-inhibit-aberrance-doublecheck): Rename from
allout-during-yank-processing.  All callers changed.
(allout-ascend): Provide for unusual case where some topic after
the first in file is at lower depth than the first.
(allout-shift-in): Ensure the offspring of the new containing
topic are exposed.
(allout-encrypt-string): Preserve the coding-system of the text,
according to that of the containing buffer.
(allout-toggle-subtree-encryption): When the text being encrypted
requires a different coding system, offer to preserve the coding
system using a file local var.