win,msi: broadcast WM_SETTINGCHANGE after install

In theory the msi should broadcast a 'WM_SETTINGCHANGE' message to all
windows after modifying the PATH environment variable. This ensures that
the new PATH is visible to other processes without restarting windows
(although it's still necessary to close and reopen active console
windows).

Unfortunately, the broadcast doesn't always happen, for unknown reasons.
That's why this patch adds a custom action that unconditionally
broadcasts a WM_SETTINGCHANGE message.

Bug: https://github.com/iojs/io.js/issues/603
PR: https://github.com/iojs/io.js/pull/613


Reviewed-by: Bert Belder <bertbelder@gmail.com>