add the ability for a query to match multiple arbitrary ranges within a single index

Right now it's easy to specify a query that will scan a range on an index:

index { a:1 }

query { a:{ $gte:5, $lte:10 } }

or a set of points on an index:

index { a:1 }

query { a:{ $in:[ 1, 2 ] } }

Using a regular expression it is also possible to specify certain combinations of ranges on an index:

index { a:1 }

query { a:{ $in:[ /^x/, /^y/ ] } }

This ticket represents functionality for easily specifying more than one arbitrary range on a single index, scanned efficiently by the query optimizer. For example on

index { a:1 }:

1) query { $or:[ { a:{ $gte:5, $lte:10 } }, { a:{ $gte:100 } } ] }

2) query { a:{ $in:[ { $gte:5, $lte:10 }, { $gte:100 } ] } }

Example 1 is not currently optimized to work as a single index scan because $or is only implemented to support more general cases where or clauses may use different indexes.

Example 2 is not an allowed query currently.