Use respond_to? with true to check inspect private/protected methods

I expect it to fix the memory leak described in: https://github.com/bmabey/database_cleaner/issues/204
But it doesn't 100% helps. 

Anyway, the problem is that starting from 1.9.3 `respond_to?` returns `true` only for public methods, so to make it work against `private` we need to add second optional parameter as `true`.