* Lib/linecache.py: don't crash on empty filename

* Lib/macpath.py: don't return trailing colon for dirname()
	(XXX won't do for volume names -- but otherwise glob(':*:*.py')
	loops forever)
	* Lib/traceback.py: print SyntaxError correctly
	* Lib/stat.py: moved to posixstat.py; added macstat.py which has
	the constants for the Mac; and created new stat.py which includes
	the right one
	* Lib/urllib.py: fix caching bug (by disabling the cache)