windows: ignore file attributes (#520)

windows: ignore file attributes (#520)

On Windows a FILE_ACTION_MODIFIED event (i.e. a Write event) is
triggered on file attribute changes, rather than some dedicates
ATTRIBUTE_CHANGED event. Looking at the docs, I don't really see a way
to distinguish between "real" write events and attribute changes. This is
very odd, but seems to be how the ReadDirectoryChangesW() API works.

The only way I can see to distinguish between the two events is to set
up two filters: one with a FILE_NOTIFY_CHANGE_ATTRIBUTES, and one
without. But that seems overly complex, and no one asked to get Chmod
events for Windows; it's not really all that interesting on Windows
anyway.

The problem is that some software (anti-virus, backup software, etc.)
can issue lots of attribute changes, causing a lot of "fake" Write
events.

So remove the FILE_NOTIFY_CHANGE_ATTRIBUTES and sysFSATTRIB flags.

This was adapted from the tilt-dev/fsnotify fork:
https://github.com/tilt-dev/fsnotify/pull/8

Fixes #487