add geoHaystack index support

lib/mongo.rb

@@ -24,6 +24,7 @@ module Mongo
   ASCENDING   =  1
   DESCENDING  = -1
   GEO2D       = '2d'
+  GEOHAYSTACK = 'geoHaystack'
 
   DEFAULT_MAX_BSON_SIZE = 4 * 1024 * 1024
 

lib/mongo/collection.rb

@@ -888,7 +888,7 @@ module Mongo
         field_spec[spec.to_s] = 1
       elsif spec.is_a?(Array) && spec.all? {|field| field.is_a?(Array) }
         spec.each do |f|
-          if [Mongo::ASCENDING, Mongo::DESCENDING, Mongo::GEO2D].include?(f[1])
+          if [Mongo::ASCENDING, Mongo::DESCENDING, Mongo::GEO2D, Mongo::GEOHAYSTACK].include?(f[1])
             field_spec[f[0].to_s] = f[1]
           else
             raise MongoArgumentError, "Invalid index field #{f[1].inspect}; " +