Windows<->Linux attribute bingo: Set Windows/Linux default attributes instead of null

[binwiederhier]

Syncany knows DOS attributes (Windows-only) and POSIX file permissions (Linux-only). When syncing files between Windows and Linux, the file the "other" attribute metadata is set to null by default.

Example:

1. A file is created on Linux with POSIX perms = rw-rw-rw-
2. The DOS attrs are set to null
3. When a Windows client downloads the file, Windows sets some default permissions (e.g. a---)
4. This is considered a change of attribute by Syncany's StatusOperation (from null to a---), so these changes are synced to the repo.
5. The Linux client downloads these changes and applies the metadata.

If more clients are connected, there might be an even more complex bingo going on.
Solution: Set default attributes for the "other" OS.

[binwiederhier]

99df0b9 should fix this, but I can't test it from a unit test. we'll need to observe two clients on Windows and Linux and see if it works.

[binwiederhier]

Well, the attributes are now correct. But there still seems to be a problem with the last modified date. Investigating

[binwiederhier]

File precision is different on Linux/ext3 (second) and Windows (millisecond). Arggh...

[binwiederhier]

Fixed by ae3afda -- making last modified time stamps second based (not millisecond based)