Fetch method name for 'whereami' directly from binding.

Pry::Method.from_str fails to find by name unbound method that was
removed from the class. As 'whereami' command needs only name of the
method it can fetch that name directly from binding without performing
lookup of the method itself.

lib/pry/default_commands/context.rb

@@ -143,11 +143,7 @@ class Pry
           i_num = 5
         end
 
-        if (meth = Pry::Method.from_binding(target))
+        meth_name = Pry::Method.method_name_from_binding(target) || "N/A"
-          meth_name = meth.name
-        else
-          meth_name = "N/A"
-        end
 
         if file != Pry.eval_path && (file =~ /(\(.*\))|<.*>/ || file == "" || file == "-e")
           raise CommandError, "Cannot find local context. Did you use `binding.pry`?"

lib/pry/method.rb

@@ -45,7 +45,7 @@ class Pry
       # @return [Pry::Method, nil]
       #
       def from_binding(b)
-        meth_name = b.eval('__method__')
+        meth_name = method_name_from_binding(b)
         if [:__script__, nil, :__binding__, :__binding_impl__].include?(meth_name)
           nil
         else
@@ -113,6 +113,14 @@ class Pry
         ([klass] + klass.ancestors).uniq
       end
 
+      # Given a `Binding` extract name of the method it originated from.
+      # Return `nil` if no such method exists.
+      # @param [Binding] b
+      # @return [Symbol, nil]
+      def method_name_from_binding(b)
+        b.eval('__method__')
+      end
+
       private
 
       # See all_from_class and all_from_obj.