WrappedModule now ignores def_delegator methods, fixes #801

If a class had most of its methods defined by def_delegators, the module extraction code would break.
This was due to Pry::WrappedModule looking for the class definition in fowardable.rb. We now
just simply reject all methods that have source_location.first =~ /forwardable\.rb/

lib/pry/wrapped_module.rb

@@ -273,7 +273,7 @@ class Pry
     # @return [Array<Pry::Method>]
     def all_relevant_methods_for(mod)
       all_methods_for(mod).select(&:source_location).
-        reject{ |x| x.name == '__class_init__' }
+        reject{ |x| x.name == '__class_init__' || method_defined_by_forwardable_module?(x) }
     end
 
     # Return all methods (instance methods and class methods) for a
@@ -298,6 +298,15 @@ class Pry
       end.flatten
     end
 
+    # Detect methods that are defined with `def_delegator` from the Forwardable
+    # module. We want to reject these methods as they screw up module
+    # extraction since the `source_location` for such methods points at forwardable.rb
+    # TODO: make this more robust as valid user-defined files called
+    # forwardable.rb are also skipped.
+    def method_defined_by_forwardable_module?(method)
+      method.source_location.first =~ /forwardable\.rb/
+    end
+
     # memoized lines for file
     def lines_for_file(file)
       @lines_for_file ||= {}