Fix broken "gcl diff cl" command. We need to use full paths, not...

gcl.py

Index: gcl.py
===================================================================
--- gcl.py	(revision 48639)
+++ gcl.py	(working copy)
@@ -1166,10 +1166,14 @@
     files = change_info.GetFileNames()
   else:
     files = GetFilesNotInCL()
-  return RunShellWithReturnCode(['svn', 'diff'] + files + args,
-                                print_output=True)[1]
 
+  root = GetRepositoryRoot()
+  cmd = ['svn', 'diff']
+  cmd.extend([os.path.join(root, x) for x in files])
+  cmd.extend(args)
+  return RunShellWithReturnCode(cmd, print_output=True)[1]
 
+
 @no_args
 def CMDsettings():
   """Prints code review settings for this checkout."""