adapter_macro should use return

[drewbanin]

Presently, adapter_macro does some munging to pick the correct macro given the active profile. This works reasonably well, but fails in the case when the underlying macro returns a value. The call stack looks like

1. macro_name() in model.sql
2. adapter_macro() in common.sql
3. {adapter}__macro_name() in macro.sql

Macro #2 converts all results to text, so non-text (eg. list, dict, number) results are mangled. This can be fixed by using the return function here

[drewbanin]

#666