RFR: JDK-8027836 Webrev script breaks for files that has been moved from a directory which now is also removed

[Magnus Ihse Bursie]

Bug: https://bugs.openjdk.java.net/browse/JDK-8027836
If the last file from a directory is moved by hg mv, the directory 
itself is removed by mercurial.

Webrev cannot handle this situation properly.

WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8027836-fix-webrev-moved-from-removed-dir/webrev.02

/Magnus