format-patch -s: add MIME encoding header if signer's name requires so

When the body of the commit log message contains a non-ASCII character,
format-patch correctly emitted the encoding header to mark the resulting
message as such.  However, if the original message was fully ASCII, the
command line switch "-s" was given to add a new sign-off, and
the signer's name was not ASCII only, the resulting message would have
contained non-ASCII character but was not marked as such.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

commit.h

@@ -61,13 +61,15 @@ enum cmit_fmt {
 	CMIT_FMT_UNSPECIFIED,
 };
 
+extern int non_ascii(int);
 extern enum cmit_fmt get_commit_format(const char *arg);
 extern void format_commit_message(const struct commit *commit,
                                   const void *format, struct strbuf *sb);
 extern void pretty_print_commit(enum cmit_fmt fmt, const struct commit*,
                                 struct strbuf *,
                                 int abbrev, const char *subject,
-                                const char *after_subject, enum date_mode);
+                                const char *after_subject, enum date_mode,
+				int non_ascii_present);
 
 /** Removes the first commit from a list sorted by date, and adds all
  * of its parents.