generally, RangeKeys() not supportable in Mad-Hatter

[steveyen]

I think, generally, RangeKeys() are not supportable in Mad-Hatter, since the query engine assumes an ordering to the keys?

n1fty/index.go

Line 89 in 7b74840

return i.rangeKeyExpressions

[abhinavdangeti]

Addressed with http://review.couchbase.org/#/c/104917/