interactive_shell: use Formula#full_name

Library/Homebrew/utils.rb

@@ -85,7 +85,7 @@ end
 def interactive_shell f=nil
   unless f.nil?
     ENV['HOMEBREW_DEBUG_PREFIX'] = f.prefix
-    ENV['HOMEBREW_DEBUG_INSTALL'] = f.name
+    ENV['HOMEBREW_DEBUG_INSTALL'] = f.full_name
   end
 
   Process.wait fork { exec ENV['SHELL'] }