Fix error message of `createSymbolicLink`.

Consider `ln` (or any other Unix tool):

    $ ln -s file1 file2
    $ ls -l file2
    lrwxrwxrwx 1 niklas niklas 5 Feb  8 03:09 file2 -> file1
    $ ln -s file1 file2
    ln: failed to create symbolic link 'file2': File exists

The file name mentioned in the error ("link2") is the one
that *could not be created*, not the content of the pointer.

`createSymbolicLink` got this wrong so far, it would print

    file1: createSymbolicLink: already exists (File exists)

which is wrong, this file doesn't already exist.

This commit fixes it.