fix path issues on mac and win for skpdiff_server.py

R=djsollen@google.com, epoger@google.com, jvanverth@google.com

Author: zachr@google.com

Review URL: https://chromiumcodereview.appspot.com/22650009

git-svn-id: http://skia.googlecode.com/svn/trunk@10719 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed