XEmacs compatibility. Doc fix.

XEmacs compatibility.  Doc fix.
(leading-code-private-22): Declare var if it's not declared yet.
(charset-bytes, charset-dimension, charset-id, charset-width)
(find-charset-region, split-char, char-width, chars-in-region)
(forward-point, decompose-composite-char, encode-coding-string)
(coding-system-p, ccl-execute-on-string, define-ccl-program):
Define funs if not defined yet.
(encode-composition-rule, find-composition): Define funs if not
loaded yet.
(ps-mule-prologue): PostScript code fix.

(ps-mule-generate-font): New arg HEADER-P.  If it is
non-nil, generate font for the header strings.
(ps-mule-prepare-font): Likewise.
(ps-mule-generate-glyphs): Likewise.
(ps-mule-string-encoding): Likewise.
(ps-mule-header-charsets): New variable.
(ps-mule-encode-header-string): New function.
(ps-mule-header-string-charsets): New function.
(ps-mule-begin-job): Check charsets in the header strings.  If there
are non-ASCII and non-Latin1 charsets, prepare fonts for them.