Fixed bugs 4385 (Nautilus doesn't gracefully handle deleting
	in-use image file), 3240 (reloading a directory doesn't update
	directory counts of the entries) and 4683 (embedded text on icon
	isn't updated when text changes) by implementing forgetting of
	file attributes and using it when appropriate.

	Also fixed various other bugs cought by testing of these fixes or
	reading the code.

	* libnautilus-extensions/nautilus-file.c:
	(nautilus_file_forget_attributes): New function that makes the
	file forget the specified attributes, including cancelling
	possible in-progress I/O for them, and kicking off new I/O if
	anyone is monitoring any of the attributes or has a pending
	call_when_ready.
	(nautilus_file_forget_attributes_internal): Forget all attributes
	of this file, *not* including cancelling in-progress I/O, or
	kicking off new I/O. This is for the benefit of NautilusDirectory
	being able to forget the attributes of all files it is monitoring
	at one go....