Properly show Gateway name in admin report

It was showing "internal name", i believe showing the Display name is best.
It used to show it like that until this commit : https://github.com/wp-e-commerce/WP-e-Commerce/commit/2307c37de20a6fb8f9c06c1badeb41c79d842f8b
Merge pull request #1500 from misulicus/patch-20

Properly show Gateway name in admin report