6939260: (fs) BasicFileAttributes.lastModifiedTime() should return last modified time with higher precision

[Alan Bateman]

File timestamps are currently returned with second resolution on 
Solaris/Linux, this is because this is what stat(2) and fstat(2) give 
us. I'd like to update this to use the nanosecond values where available.

The webrev with the changes is here:

http://cr.openjdk.java.net/~alanb/6939260/webrev/

Thanks,

Alan.