package imports in module headers

Test confirms support for package imports in module headers
Regressing before / after shows this change didn't break anything

```
$ diff before.log after.log 
2008c2008
<                mod_inst_pkg: ==> Failed - running iverilog.
---
>                mod_inst_pkg: Passed.
2011c2011
<   Total=2006, Passed=1999, Failed=7, Not Implemented=0, Expected Fail=0
---
>   Total=2006, Passed=2000, Failed=6, Not Implemented=0, Expected Fail=0
```