8028270: Files.readSymbolicLink calls AccessController directly so security manager can't grant the permission

[Alan Bateman]

This is a follow-up to Martin's mail of yesterday where he pointed out 
that the implementations of readSymbolicLink are doing the permission 
check by calling AccessController.checkPermission directly. The bug 
means the security manager doesn't get a chance to grant the permission.

Here's the webrev to fix this (and also expand the CheckPermissions test 
to cover this case, the lack of the a test case is how this one slipped 
through).

http://cr.openjdk.java.net/~alanb/8028270/webrev/

-Alan.