* tests/static.at: Larger rewrite to make work on w32: Use three

* tests/static.at: Larger rewrite to make work on w32: Use three
different prefixes instead of three libdirs, so the moving of
the DLLs works as expected.  Adjust all code.  Since now
$libdirI/../bin is distinct from the directory of the installed
program, take care than on w32 PATH contains the needed bindirs,
in appropriate order.
Report by Charles Wilson.