* spawn.cc (find_exec): Only return files with execute permission set

	* spawn.cc (find_exec): Only return files with execute permission set
	if ntsec is on.  Don't check execute permission of Windows batch files.
	(av::fixup): Handle empty files gracefully.  Drop execute permission
	test here.
	* path.cc (suffix_scan::next): Don't skip any suffix on first run.