[L5] Clarification of INTENT(OUT) usage

[mlange05]

Issue originally raised by P. Marguinaud in GPU adapation additions. It pertains to rule L5:

>>PM: Structures like YDVARS which contain some pointers can have the INTENT(IN) attribute, and
have their pointed values modified. This is a problem, as we will have such structures everywhere
in the code.
Furthermore, using the ``INTENT(OUT)`` attribute for such variables may cause some compilers 
(eg NAG) to wipe their contents.
And YDVARS also contains some metadata that should remain constant. I think we do not have any
other choice but to declare YDVARS (and other similar structures) with ``INTENT(IN)`` everywhere.
<<