JS: add a ConditionalHandle to control execution of condtionalEvents

This allows waitUntil() using code to be killed by passing the same handle to
killEvent.  This is very similar to the EventHandle-based API for waiting events.

Signed-off-by: Harvey Harrison <harvey.harrison@ausenco.com>
JS: Process is now entirely an internal implementation detail, remove public access

Signed-off-by: Harvey Harrison <harvey.harrison@ausenco.com>
JS: update version to 2014-19

Signed-off-by: Harvey Harrison <harvey.harrison@ausenco.com>