Aggregations: the `children` agg didn't take deleted document into account

The live docs that is passed down was ignored by the filter impl. Now the children filter gets wrapped with ApplyAcceptedDocsFilter, so live docs are actually applied.

This issue was reported via the user list: https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!msg/elasticsearch/sybogZsMFso/f_UW4Zv01ZIJ