Bug fix: MultiSearch was returning derived types as base type (as specified in generic)

This fix adds the ConcreteTypeConverter when multiple Types are passed in. Due to my lack of intimate knowledge of how all of the code works, my fix may look a little kludgy/hacky - I wanted to avoid breaking existing functionality with the multisearch - please feel free to revise/clean-up as needed.
Merge pull request #352 from freshmaker74/patch-2

Bug fix: MultiSearch was returning derived types as base type (as specif...