Regression fix + Binary chunk DoString

- Fixes regressions introduced by commit 4cfc1f2b2e8e834cfeaffcff85b0f22f2cb78f74, due to generic collection exceptions in Metatables.checkMemberCache and Metatables.setMemberCache. __(Sorry for the rookie mistake. Now all the NUnit tests are in green.)__

- Simplified DoString for strings by replacing DoString(string,string)
and DoString(string) by a single method DoString(string[,string]).

- Added DoString(byte[][,string]) to allow for usage of binary chunks.