pretty.h: move has_non_ascii() declaration from commit.h

The function is defined in pretty.c, so this moves the declaration to
a more logical place.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pretty.h

@@ -153,6 +153,8 @@ int commit_format_is_empty(enum cmit_fmt);
 /* Make subject of commit message suitable for filename */
 void format_sanitized_subject(struct strbuf *sb, const char *msg, size_t len);
 
+int has_non_ascii(const char *text);
+
 /*
  * Set values of fields in "struct process_trailer_options"
  * according to trailers arguments.