_include and _revinclude not working when included param references array

[cmoesel]

If the included param references a field that is an array, then the included results are not returned (for example, _include=Observation:performer). This is because MongoDB's left-join (a.k.a. $lookup) doesn't work with array fields. You need to unwind the arrays and then group them back together again.

See:

• https://jira.mongodb.org/browse/SERVER-21469
• http://stackoverflow.com/questions/34967482/lookup-on-objectids-in-an-array