Require pmail; delete compiler defvars.

Require pmail; delete compiler defvars.
Delete most declare-function calls.
(pmail-keywords, pmail-deleted-label, pmail-attributes): Vars deleted.
(pmail-attribute-p, pmail-keyword-p): Fns deleted.
(pmail-keywords, pmail-parse-file-keywords, pmail-install-keyword):
(pmail-force-make-label, pmail-quote-label-name): Fns deleted.
(pmail-last-label, pmail-last-multi-labels): Vars moved from pmail.el.
(pmail-read-label): Don't switch buffers, don't parse file keywords.
(pmail-set-label): Major rewrite.
(pmail-next-labeled-message): Call pmail-get-labels and match it.