Change the way imported binary variables are imported, from
`reflect.ValueOf(val)` to `reflect.ValueOf(&val).Elem()`, to allow these
variables to be set from the interpreter.
Regenerate stdlib packages accordingly.
Ensure that binary value is forwarded if it exists.
Add tests.
This fixes problems due to storing binary symbols as interfaces{}
instead of concrete type, which confuses lookup functions to retrieve
methods etc. in reflect.
