tests/test-diffdir.out

Fix up copy command to behave more like regular "cp".
In addition to recording changes, copy now updates the working
directory.

diff -r 3903775176ed b
--- /dev/null
+++ b/b
@@ -0,0 +1,1 @@
+123
diff -r 3903775176ed b
--- /dev/null
+++ b/b
@@ -0,0 +1,1 @@
+123