(unicodedata-file): New.

(unicodedata-file): New.
(unicode-data): New (adapted from unicode branch).
(describe-char): Use it.  Print char's unicode differently.  Avoid
elements with null cadr when formatting list.  Clarify error
message when used in Help buffer.
(button): Require when compiling.
(describe-char-after): Alias for obsolete command.