[7u6] Request for approval for CR 7103889: (fs) Reduce String concatenation when iterating over directory

[Seán Coffey]

Makes sense to backport some recent work done in JDK 8 to 7u.

identical changes. JDK 8 changeset : 
http://hg.openjdk.java.net/jdk8/tl/jdk/rev/bb2b9a8b6e77
bug report : http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7103889

regards,
Sean.