fetchpatch: ignores file renames

If the patch renames a file, and contains:

```
rename from libraries/base/GHC/Event/Clock.hsc
rename to libraries/base/GHC/Clock.hsc
```

Then using `patch -p1 < foobar.patch` works as expected, while using fetchpatch no rename happens.

cc @vcunat @aszlig @copumpkin @fpletz @globin 