Coccinelle: Add a new mode named 'chain'

spatch now returns -1 when a virtual rule (given with
-D on the command line) is not defined in the semantic patch.

Using this spatch feature, coccicheck is now
tries several modes by default, in the order:
	patch, report, context, org

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