Adding constant for line.separator and friends

[Alan Bateman]

Ulf Zibis wrote:
> :
> At least, IMO, fileSeparator() and pathSeparator() would belong to 
> java.io.File or java.nio.file.FileSystem.
As I think Martin pointed out, File.separator and File.pathSeparator 
have always been there. They should of course have been methods rather 
than fields. In theory the separators could be more than a single 
character but it's hard to find examples. One could debate as to if File 
was the right place to define the path separator as the concept of path 
is more of a shell or system concept. It's also worth pointing out that 
FileSystem already defines a getSeparator method. In the case of the 
default FileSystem then it will return the same as File.separator. When 
additional providers are installed then they may use different 
separators of course.

-Alan.