environment inheritance and append mode output redirection 

Hi Saleyn,

my friend David and I addressed a couple of problems in exec:run_link/2 while:
- while spawning a process, the environment of the caller was not inherited,
- while defining an stdout/stderr redirection, the append mode was ignored,

Would it be good for you to merge this in your main master project?

Thank you, let us know.
Enrico