Use SHChangeNotifyRegister to monitor directories for changes

[derceg]

ReadDirectoryChangesW

Currently, ReadDirectoryChangesW is used to monitor directories for changes. There are a few disadvantages of using this method:

• It only monitors filesystem folders. Directories such as the recycle bin can't be monitored (see #103).
• The current implementation uses a background thread, which introduces extra complexity.

SHChangeNotifyRegister

SHChangeNotifyRegister is an alternative way of monitoring directories for changes. It has the following advantages compared to ReadDirectoryChangesW:

• All directories can be monitored. The function accepts a pidl, rather than a folder handle.
• Change notifications are sent as window messages, meaning there would only be a single thread involved.

Known issues

• In Windows 7 at least, no change notifications appear to be sent for the Recycle Bin unless the user has the folder open in Windows Explorer. Even if reliably monitoring the recycle bin for changes isn't possible, using SHChangeNotifyRegister should still be beneficial, as it will allow other non-filesystem directories (e.g. library folders) to be monitored properly.