Reviewed-by: chegar, sherman

Reviewed-by: xdono

Reviewed-by: sherman

Reviewed-by: darcy, weijun

6876541: (file) Files.walkFileTree(...): no SecurityException if read access to the starting file is denied
Reviewed-by: chegar

6868627: (spec) Files.walkFileTree doesn't make it clear that uncaught errors and exceptions are propagated
Reviewed-by: sherman

6844313: New I/O: File timestamps should be represented by a FileTime rather than a long+TimeUnit
Reviewed-by: sherman

4313887: New I/O: Improved filesystem interface
4607272: New I/O: Support asynchronous I/O
Reviewed-by: sherman, chegar