RFR: JDK-8026061 - File.createTempFile fails if prefix is absolute path

[Dan Xu]

Hi,

This is a backport request towards 7u-dev repository on bug JDK-8025128 
that I fixed several days ago. It is going to keep the method, 
File.createTempFile(), backward compatible. Please help review it. Thanks!

Bug: https://bugs.openjdk.java.net/browse/JDK-8026061
Webrev: http://cr.openjdk.java.net/~dxu/8026061/webrev/

-Dan