hg: code-tools/trees: 7901672: trees extension broken after upgrade to mercurial 3.8.1

[jonathan.gibbons at oracle.com]

Changeset: af82295c9167
Author:    erikj
Date:      2017-06-02 18:22 -0700
URL:       http://hg.openjdk.java.net/code-tools/trees/rev/af82295c9167

7901672: trees extension broken after upgrade to mercurial 3.8.1
Reviewed-by: ihse, jjg

! trees.py