memDBCurrentGen RDS types get wrong or no pricing

[20goto10]

For types db.m2.xlarge, db.m2.2xlarge, db.m2.4xlarge, and db.cr1.8xl the pricing gem is not correctly identifying the on-demand multi-AZ prices. The gem's single-AZ prices get overwritten by the correct multi-AZ ones, while the gem's multi-AZ prices are never populated.

I was able to fix this by adjusting line 254 of amazon-pricing.rb --

          if url.include?("multiAZ")
            is_multi_az = true
          else
            is_multi_az = is_multi_az? type["name"]
          end              

The URL include? hack replaces the Oracle-only URL hack that was already there. I've verified that this fixes on-demand pricing for these instance types, but I haven't checked it against the other rate types as that's outside my concern. But I hope someone can replace this hack with something a little more elegant.