Cache: Fix -ESTALE when inter-directory renaming replaces an existing fi...

...le.

Test case :

echo toto > dir1/toto
cat dir1/toto
echo titi > dir2/titi
cat dir2/titi
mv dir2/titi dir1/toto
cat dir1/toto       <<<<<------ open returns -ESTALE

Signed-off-by: Simon Derr <simon.derr@bull.net>