nitg: Added PNaCl support for Nit

Signed-off-by: Djomanix <johan.kayser@viacesi.fr>
nitg: Added comment for exec_and_check

Signed-off-by: Djomanix <johan.kayser@viacesi.fr>
Example : Added a pnacl example

Signed-off-by: Djomanix <johan.kayser@viacesi.fr>