* src/character.c (Fmax_char): Accept an optional argument
UNICODE, and, if non-nil, return the maximum codepoint defined by
Unicode.
* lisp/emacs-lisp/comp.el (comp-known-type-specifiers): Update the
signature of 'max-char'.
* etc/NEWS:
* doc/lispref/nonascii.texi (Character Codes): Update the
documentation of 'max-char'.