Allow to run a program with arguments from a proc.

you can now do, inside a Felix program:

Dynlink::run_program$ list ("dlmain", "arg1", "arg2");

which will run the program dlmain with arguments,
as a subroutine. There are some caveats and restrictions:
the program can't use fibres and schannels, and at present
if System::exit is called it will exit the whole process
(not just return from the run_program call).

The program must be available as shared library.