Coccinelle: Add null/kmerr.cocci

This semantic patch looks for kmalloc etc that are not followed by a
NULL check.  It only gives a report in the case where there is some
error handling code later in the function, which may be helpful
in determining what the error handling code for the call to kmalloc etc
should be.

Signed-off-by: Nicolas Palix <npalix@diku.dk>
Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Michal Marek <mmarek@suse.cz>