(normalize_filename): Always lower-case drive letters, even on systems

(normalize_filename): Always lower-case drive letters, even on systems
	that preserve case in filenames.
(sys_rename): Do not delete newname if only changing case.  On Windows
	95, use our version of mktemp (not the MSVC version) and give
	the temp name a long extension to ensure the final rename works
	as expected.