Fix compatibility with svn 1.7.

scm.py

Index: scm.py
diff --git a/scm.py b/scm.py
index da094fb596825f738e58a985f5c197e609151559..0f31d1c4bffb300e017a485ff793fa5a5a0a14a8 100644
--- a/scm.py
+++ b/scm.py
@@ -578,7 +578,11 @@ class SVN(object):
 
     # Use .text when the item is not optional.
     result['Path'] = entry.attrib['path']
-    result['Revision'] = int(entry.attrib['revision'])
+    rev = entry.attrib['revision']
+    try:
+      result['Revision'] = int(rev)
+    except ValueError:
+      result['Revision'] = None
     result['Node Kind'] = entry.attrib['kind']
     # Differs across versions.
     if result['Node Kind'] == 'dir':