Throw error when @recurse queries contain nested fields.

[martinmr]

This change is 

[MichelDiz]

Reviewed 2 of 2 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved

[manishrjain]

Reviewed 2 of 2 files at r1.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @martinmr)

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query/recurse.go, line 204 at r1 (raw file):

	for _, child := range sg.Children {
		if len(child.Children) > 0 {
			return x.Errorf("@recurse queries do not support nested predicates")

recurse queries do not allow nested predicates, they must be specified on one level.