WHEN fails if used in child graph
WHEN fails if used in child graph

Thor refused to run WHEN in a child query, because it was marked as
a global activity, but WHEN(dataset, ..) can be executed in a child query
context

Signed-off-by: Jake Smith <b20121000db38205734e8ca1c74fe9668b08552a@lexisnexis.com>

RussWhitehead/HPCC-Platform,RussWhitehead/HPCC-Platform,afishbeck/HPCC-Platform,afishbeck/HPCC-Platform,RussWhitehead/HPCC-Platform,RussWhitehead/HPCC-Platform,RussWhitehead/HPCC-Platform,afishbeck/HPCC-Platform,RussWhitehead/HPCC-Platform,afishbeck/HPCC-Platform,afishbeck/HPCC-Platform,RussWhitehead/HPCC-Platform,afishbeck/HPCC-Platform