[9] RFR 8177969: Faster FilePermission::implies by avoiding the use of Path::relativize

[Weijun Wang]

http://cr.openjdk.java.net/~weijun/8177969/webrev.00/
This new implementation of containsPath(Path,Path) uses the logic of 
Path::relativize without directly calling it, which is much faster now.

Thanks
Max