6907737: (file) FileVisitor and Files.walkFileTree issues

[Alan Bateman]

A few weeks ago I mentioned that we needed to fix a several issues with 
Files.walkFileTree/FileVisitor.  The list is here:
    http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6907737

I'd like to fix these as a batch to avoid too much disruption. The 
webrev with the proposed changes is here:
   http://cr.openjdk.java.net/~alanb/6907737/webrev/

In addition to this, there is also a one-line change in the langtools 
repo (to add the new parameter to preVisitDirectory). I'll push that at 
the same time.

Thanks,

-Alan.