facebook/presto — pull request #1535 by miniway (2014-08-05 17:48:29+00:00)
Title: Let each type decide coerce and common super type

When adding a type from plugin, the type need to supply
whether it can coerce from given type and have a common super type

For example, if we add a CustomRegexpType and related UDFs, the `FunctionRegistry` need to know the type can coerce from `VARCHAR`