(quail-store-decode-map-key): Store a

(quail-store-decode-map-key): Store a
translated character too.
(quail-char-equal-p): New function.
(quail-find-key1): Check character equality by quail-char-equal-p.
(quail-decode-map-generated): New variable.
(quail-find-key): Check quail-decode-map-generated and re-generate
a decode map if necessary.