Pry::CodeObject, Pry::WrappedModule: introduce safe_to_evaluate? method

Unsure where to put safe_to_evaluate? method, so it's currently duplicated in
both the mentioned modules. If we can simply switch to a defined?(str) != "method" test
then we could put the method on Pry::Method.looks_like_a_method?(str, binding) and call it from both locations, avoiding duplication.

https://www.evernote.com/shard/s130/sh/4e839419-387e-43ab-81d5-06f87aa2cbac/2c640432e3ecccb2035c69c347f63af1