Large file support

In order to properly support files >2GB, we need to change the signature of `seek` and `tell` method for `sys.io.FileInput`, using Float instead of Int, which is more easy to handle than Int64, and provides files sizes up to 9007 TB.

seek() is not a problem, because passing Int will still work it might have 0 impact on user code, unless someone overrides it.
tell() will change the return type so it might break some code relying on it.

Alternative is to add seekLarge() tellLarge() operations but I don't like much people having to change their code once their hit 2GB limit.