sourceMaps non-string option while sourceComments='map' causes crash

Finally fixes #337, the bug is caused by the grunt-sass library setting `sourceComments` to `map` while leaving `sourceMaps` as `undefined`. The way I chose to fix this was to set `sourceMaps` to `''` as that seems to be an acceptable way to pass this option to libsass (tbh I don't know what it ends up doing with it but I can confirm it works and I think the tests might also be doing this).

Also, I changed the binary loader section and removed the *obj.target* directory as the buillds end up being linked into the directory above that and it should be the proper place to load it from. I also added the *Debug* directory as that's where they end upwith `--debug` and I needed that to get some lldb line number magic out of this crash.