Nim incorrectly import/include files relative to the destination of a symlinked file

``` sh
mkdir d
cat >d/t.nim<<E
import m
echo c
E
cat >d/m.nim<<E
const c* = "from d"
E
ln -s d/t.nim .
cat >m.nim<<E
const c* = "outside of d"
E
nim c -r t
```
The output is ``from d``, while I would expect the output should be ``outside of d``.