xquery:fork-join, module imports

```xquery
(: x.xq :)
import module namespace x = 'x' at 'x.xqm';
xquery:fork-join((1 to 16) ! fn() { sum($x:V) })

(: x.xqm :)
module namespace x = 'x';
declare variable $x:V := (1 to 1000000) ! math:sqrt(.);
```

…results in:

```
Stopped at x.xqm, 2/18:
[XQDY0054] Static variable depends on itself: $x:V
```