[kernel] Remove uses of deprecated API.

Signed-off-by: Stéphane Galland <galland@arakhne.org>
[demos] Use the reference test operator when testing if null.

Signed-off-by: Stéphane Galland <galland@arakhne.org>
[demos] Fixing the name of the inherited Initialize event handler.

Since the SARL code generator has changed, the names of the generated
event handlers have indexes starting from 0 (1 in the previous version).

see #1.

Signed-off-by: Stéphane Galland <galland@arakhne.org>