Mark char* fields in struct cgit_page as const

Signed-off-by: John Keeping <john@keeping.me.uk>

ui-plain.c

@@ -100,8 +100,9 @@ static int print_object(const unsigned char *sha1, const char *path)
 	ctx.page.etag = sha1_to_hex(sha1);
 	cgit_print_http_headers(&ctx);
 	html_raw(buf, size);
+	/* If we allocated this, then casting away const is safe. */
 	if (freemime)
-		free(ctx.page.mimetype);
+		free((char*) ctx.page.mimetype);
 	return 1;
 }