Process: Fixed documentation for kill().

predef::kill() returns int(0..1) (not void).

Thanks to Per Cederqvist <cederp@opera.com> for the report.

Fixes [LysLysKOM 20889011].

Also strengthens the return type from int to int(0..1).
There MUST NOT be more than one extension of the same type. RFC 5246 section 7.4.1.4.